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Signorini problem Each system expresses a unilateral constraint, in the sense that they express the physical impossibility of the elastic body to penetrate into the surface where it rests: the ambiguity is not only in the unknown values non-zero quantities must satisfy on the contact set but also in the fact that it is not a priori known if a point belonging to that set satisfies the system of boundary conditions or . The set of points where is satisfied is called the area of support of the elastic body on formula_5, while its complement respect to formula_5 is called the area of separation. The above formulation is "general" since the Cauchy stress tensor i.e. the constitutive equation of the elastic body has not been made explicit: it is equally valid assuming the hypothesis of linear elasticity or the ones of nonlinear elasticity. However, as it would be clear from the following developments, the problem is inherently nonlinear, therefore "assuming a linear stress tensor does not simplify the problem". The form assumed by Signorini and Fichera for the elastic potential energy is the following one (as in the previous developments, the Einstein notation is adopted) where The Cauchy stress tensor has therefore the following form and it is "linear" with respect to the components of the infinitesimal strain tensor; however, it is not homogeneous nor isotropic | https://en.wikipedia.org/wiki?curid=22194510 |
Signorini problem As for the section on the formal statement of the Signorini problem, the contents of this section and the included subsections follow closely the treatment of Gaetano Fichera in , , and also : obviously, the exposition focuses on the basics steps of the proof of the existence and uniqueness for the solution of problem , , , and , rather than the technical details. The first step of the analysis of Fichera as well as the first step of the analysis of Antonio Signorini in is the analysis of the potential energy, i.e. the following functional where formula_27 belongs to the set of admissible displacements formula_41 i.e. the set of displacement vectors satisfying the system of boundary conditions or . The meaning of each of the three terms is the following was able to prove that the admissible displacement formula_27 which minimize the integral formula_43 is a solution of the problem with ambiguous boundary conditions , , , and , provided it is a formula_44 function supported on the closure formula_45 of the set formula_2: however Gaetano Fichera gave a class of counterexamples in showing that in general, admissible displacements are not smooth functions of these class | https://en.wikipedia.org/wiki?curid=22194510 |
Signorini problem Therefore, Fichera tries to minimize the functional in a wider function space: in doing so, he first calculates the first variation (or functional derivative) of the given functional in the neighbourhood of the sought minimizing admissible displacement formula_47, and then requires it to be greater than or equal to zero Defining the following functionals and the preceding inequality is can be written as This inequality is the variational inequality for the Signorini problem. | https://en.wikipedia.org/wiki?curid=22194510 |
Chlorinated polycyclic aromatic hydrocarbon Chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs) are a group of compounds comprising polycyclic aromatic hydrocarbons with two or more aromatic rings and one or more chlorine atoms attached to the ring system. Cl-PAHs can be divided into two groups: chloro-substituted PAHs, which have one or more hydrogen atoms substituted by a chlorine atom, and chloro-added Cl-PAHs, which have two or more chlorine atoms added to the molecule. They are products of incomplete combustion of organic materials. They have many congeners, and the occurrences and toxicities of the congeners differ. Cl-PAHs are hydrophobic compounds and their persistence within ecosystems is due to their low water solubility. They are structurally similar to other halogenated hydrocarbons such as polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs). Cl-PAHs in the environment are strongly susceptible to the effects of gas/particle partitioning, seasonal sources, and climatic conditions. Chlorinated polycyclic aromatic hydrocarbons are generated by combustion of organic compounds. Cl-PAHs enter the environment from a multiplicity of sources and tend to persist in soil and in particulate matter in air. Environmental data and emission sources analysis for Cl-PAHs reveal that the dominant process of generation is by reaction of PAHs with chlorine in pyrosynthesis | https://en.wikipedia.org/wiki?curid=22201177 |
Chlorinated polycyclic aromatic hydrocarbon Cl-PAHs have commonly been detected in tap water, fly ash from an incineration plant for radioactive waste, emissions from coal combustion and municipal waste incineration, automobile exhaust, snow, and urban air. They have also been detected in electronic wastes, workshop-floor dust, vegetation, and surface soil collected from the vicinity of an electronic waste (e-waste) recycling facility and in surface soil from a chemical industrial complex (comprising a coke-oven plant, a coal-fired power plant, and a chlor-alkali plant), and agricultural areas in central and eastern China. In addition, the combustion of polyvinylchloride and plastic wrap made from polyvinylidene chloride result in the production of Cl-PAHs, suggesting that combustion of organic materials including chlorine is a possible source of environmental pollution. A specific class of Cl-PAHs, polychlorinated naphthalenes (PCNs), are persistent, bioaccumulative, and toxic contaminants that have been reported to occur in a wide variety of environmental and biological matrixes. Cl-PAHs with three to five rings have been reported to occur in air from road tunnels, sediment, snow, and kraft pulp mills. Recently, the occurrence of particulate Cl-PAHs has been investigated. Results have shown that most particulate Cl-PAH concentration detected in urban air tended to be high in colder seasons and low in warmer seasons | https://en.wikipedia.org/wiki?curid=22201177 |
Chlorinated polycyclic aromatic hydrocarbon This study also determined through compositional analysis that relatively low molecular weight Cl-PAHs dominated in warmer seasons and high molecular weight Cl-PAHs dominated in colder seasons. Some Cl-PAHs have structural similarities to dioxins, they are suspected of having similar toxicities. These types of compounds are known to be carcinogenic, mutagenic, and teratogenic. Toxicological studies have shown that some Cl-PAHs possess greater mutagenicity, aryl-hydorcarbon receptor activity, and dioxin-like toxicity than the corresponding parent PAHs. The relative potency of three ring Cl-PAHs was found to increase with increasing degree of chlorination as well as with increasing degree of chlorination. However, the relative potencies of the most toxic Cl-PAHs assessed up to now have been found to be 100,000-fold lower than the relative potency of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Even though Cl-PAHs aren’t as toxic as TCDD, it has been determined using recombinant bacterial cells that the toxicities of exposure to Cl-PAHs based on AhR activity were approximately 30-50 times higher than that of dioxins. Cl-PAHs demonstrate a high enough toxicity to be a potential health risk to human populations that come into contact with them. One of the well-established mechanisms by which chlorinated polycyclic aromatic hydrocarbons can exert their toxic effects is via the function of the aryl hydrocarbon receptor (AhR). The AhR-mediated activities of Cl-PAHs have been determined by using yeast assay systems | https://en.wikipedia.org/wiki?curid=22201177 |
Chlorinated polycyclic aromatic hydrocarbon Aryl Hydrocarbon Receptor (AhR) is a cytosolic, ligand-activated transcription receptor. Cl-PAHs have the ability to bind to and activate the AhR. The biological pathway involves translocation of the activated AhR to the nucleus. In the nucleus, the AhR binds with the AhR nuclear translator protein to form a heterodimer. This process leads to transcriptional modulation of genes, causing adverse changes in cellular processes and function. Several Cl-PAHs have been determined to be AhR-active. One such Cl-PAH, 6-chlorochrysene, has been shown to have a high affinity for the Ah receptor and to be a potent AHH inducer. Therefore, Cl-PAHs may be toxic to humans, and it is important to better understand their behavior in the environment. Several Cl-PAHs have also been found to exhibit mutagenic activity toward "Salmonella typhimurium" in the Ames assay. | https://en.wikipedia.org/wiki?curid=22201177 |
Propellant depot An orbital propellant depot is a cache of propellant that is placed in orbit around Earth or another body to allow spacecraft or the transfer stage of the spacecraft to be fueled in space. It is one of the types of space resource depots that have been proposed for enabling infrastructure-based space exploration. Many different depot concepts exist depending on the type of fuel to be supplied, location, or type of depot which may also include a propellant tanker that delivers a single load to a spacecraft at a specified orbital location and then departs. In-space fuel depots are not necessarily located near or at a space station. Potential users of in-orbit refueling and storage facilities include space agencies, defense ministries and communications satellite or other commercial companies. Satellite servicing depots would extend the lifetime of satellites that have nearly consumed all of their orbital maneuvering fuel and are likely placed in a geosynchronous orbit. The spacecraft would conduct a space rendezvous with the depot, or "vice versa", and then transfer propellant to be used for subsequent orbital maneuvers. In 2011, Intelsat showed interest in an initial demonstration mission to refuel several satellites in geosynchronous orbit, but all plans have been since scrapped. A low earth orbit (LEO) depot's primary function would be to provide propellant to a transfer stage headed to the moon, Mars, or possibly a geosynchronous orbit | https://en.wikipedia.org/wiki?curid=22202480 |
Propellant depot Since all or a fraction of the transfer stage propellant can be off-loaded, the separately launched spacecraft with payload and/or crew could have a larger mass or use a smaller launch vehicle. With a LEO depot or tanker fill, the size of the launch vehicle can be reduced and the flight rate increased—or, with a newer mission architecture where the beyond-Earth-orbit spacecraft also serves as the second stage, can facilitate much larger payloads—which may reduce the total launch costs since the fixed costs are spread over more flights and fixed costs are usually lower with smaller launch vehicles. A depot could also be placed at Earth-Moon Lagrange point 1 (EML-1) or behind the Moon at EML-2 to reduce costs to travel to the moon or Mars. Placing a depot in Mars orbit has also been suggested. For rockets and space vehicles, propellants usually take up 2/3 or more of their total mass. Large upper-stage rocket engines generally use a cryogenic fuel like liquid hydrogen and liquid oxygen (LOX) as an oxidizer because of the large specific impulse possible, but must carefully consider a problem called "boil off". The boil off from only a few days of delay may not allow sufficient fuel for higher orbit injection, potentially resulting in a mission abort. Lunar or Mars missions will require weeks to months to accumulate tens of thousands to hundreds of thousands of kilograms of propellant, so additional equipment may be required on the transfer stage or the depot to mitigate boiloff | https://en.wikipedia.org/wiki?curid=22202480 |
Propellant depot Non-cryogenic, earth-storable liquid rocket propellants including RP-1 (kerosene), hydrazine and nitrogen tetroxide (NTO), and mildly cryogenic, space-storable propellants like liquid methane and liquid oxygen, can be kept in liquid form with less boiloff than the cryogenic fuels, but also have lower specific impulse. Additionally, gaseous or supercritical propellants such as those used by ion thrusters include xenon, argon, and bismuth. Ex-NASA administrator Mike Griffin commented at the 52nd AAS Annual Meeting in Houston, November 2005, that "at a conservatively low government price of $10,000/kg in LEO, 250 MT of fuel for two missions per year is worth $2.5 B, at government rates." If one assumes that a 130 metric tonne launch vehicle could be flown twice a year for $2.5B, the price is about $10,000/kg. In the depot-centric architecture, the depot is filled by tankers, and then the propellant is transferred to an upper stage prior to orbit insertion, similar to a gas station filled by tankers for automobiles. By using a depot, the launch vehicle size can be reduced and the flight rate increased. Since the accumulation of propellant may take many weeks to months, careful consideration must be given to boiloff mitigation. In simple terms, a passive cryogenic depot is a transfer stage with stretched propellant tanks, additional insulation, and a sun shield. In one concept, hydrogen boiloff is also redirected to reduce or eliminate liquid oxygen boiloff and then used for attitude control, power, or reboost | https://en.wikipedia.org/wiki?curid=22202480 |
Propellant depot An active cryogenic depot is a passive depot with additional power and refrigeration equipment/cryocoolers to reduce or eliminate propellant boiloff. Other active cryogenic depot concepts include electrically powered attitude control equipment to conserve fuel for the end payload. In the heavy lift architecture, propellant, which can be two thirds or more of the total mission mass, is accumulated in fewer launches and possibly shorter time frame than the depot centric architecture. Typically the transfer stage is filled directly and no depot is included in the architecture. For cryogenic vehicles and cryogenic depots, additional boiloff mitigation equipment is typically included on the transfer stage, reducing payload fraction and requiring more propellant for the same payload unless the mitigation hardware is expended. Heavy Lift is compared with using Commercial Launch and Propellant Depots in this power point by Dr. Alan Wilhite given at FISO Telecon. Both theoretical studies and funded development projects that are currently underway aim to provide insight into the feasibility of propellant depots. Studies have shown that a depot-centric architecture with smaller launch vehicles could be less expensive than a heavy-lift architecture over a 20-year time frame. The cost of large launch vehicles is so high that a depot able to hold the propellant lifted by two or more medium-sized launch vehicles may be cost effective and support more payload mass on beyond-Earth orbit trajectories | https://en.wikipedia.org/wiki?curid=22202480 |
Propellant depot In a 2010 NASA study, an additional flight of an Ares V heavy launch vehicle was required to stage a US government Mars reference mission due to 70 tons of boiloff, assuming 0.1% boiloff/day for hydrolox propellant. The study clearly identified the need to decrease the design boiloff rate by an order of magnitude or more. Approaches to the design of low Earth orbit (LEO) propellant depots were also discussed in the 2009 Augustine report to NASA, which "examined the [then] current concepts for in-space refueling." The report determined there are essentially two approaches to refueling a spacecraft in LEO: Both approaches were considered feasible with 2009 spaceflight technology, but anticipated that significant further engineering development and in-space demonstration would be required before missions could depend on the technology. Both approaches were seen to offer the potential of long-term life-cycle savings. Beyond theoretical studies, since at least 2017, SpaceX has undertaken funded development of an interplanetary set of technologies. While the interplanetary mission architecture consists of a combination of several elements that are considered by SpaceX to be key to making long-duration beyond Earth orbit (BEO) spaceflights possible by reducing the cost per ton delivered to Mars by multiple orders of magnitude over what NASA approaches have achieved, refilling of propellants in orbit is one of the four key elements | https://en.wikipedia.org/wiki?curid=22202480 |
Propellant depot In a novel mission architecture, the SpaceX design intends to enable the long-journey spacecraft to expend almost all of its propellant load during the launch to low Earth orbit while it serves as the second stage of the SpaceX Starship, and then after refilling on orbit by multiple Starship tankers, provide the large amount of energy required to put the spacecraft onto an interplanetary trajectory. The Starship tanker is designed to transport approximately of propellant to low Earth orbit. A second propellant tanker concept is underway. United Launch Alliance (ULA) has a proposed Advanced Cryogenic Evolved Stage (ACES) tanker—a concept that dates back to work by Boeing in 2006, sized to transport up to of propellant—in early design with first flight planned for no earlier than 2023, with initial usage as a propellant tanker potentially beginning in the mid-2020s. Because a large portion of a rocket is propellant at time of launch, proponents point out several advantages of using a propellant depot architecture. Spacecraft could be launched unfueled and thus require less structural mass, or the depot tanker itself could serve as the second-stage on launch when it is reusable. An on-orbit market for refueling may be created where competition to deliver propellant for the cheapest price takes place, and it may also enable an economy of scale by permitting existing rockets to fly more often to refuel the depot | https://en.wikipedia.org/wiki?curid=22202480 |
Propellant depot If used in conjunction with a mining facility on the moon, water or propellant could be exported back to the depot, further reducing the cost of propellant. An exploration program based on a depot architecture could be cheaper and more capable, not needing a specific rocket or a heavy lift such as the SLS to support multiple destinations such as the Moon, Lagrange points, asteroids, and Mars. NASA studies in 2011 showed cheaper and faster alternatives than the Heavy Lift Launch System and listed the following advantages: Propellant depots were proposed as part of the Space Transportation System (along with nuclear "tugs" to take payloads from LEO to other destinations) in the mid-1960s. In October 2009, the Air Force and United Launch Alliance (ULA) performed an experimental on-orbit demonstration on a modified Centaur upper stage on the DMSP-18 launch to improve "understanding of propellant settling and slosh, pressure control, RL10 chilldown and RL10 two-phase shutdown operations." "The light weight of DMSP-18 allowed of remaining LO and LH propellant, 28% of Centaur’s capacity," for the on-orbit demonstrations. The post-spacecraft mission extension ran 2.4 hours before executing the deorbit burn. NASA's Launch Services Program is working on an ongoing slosh fluid dynamics experiments with partners called CRYOTE. , ULA is also planning additional in-space laboratory experiments to further develop cryogenic fluid management technologies using the Centaur upper stage after primary payload separation | https://en.wikipedia.org/wiki?curid=22202480 |
Propellant depot Named CRYOTE, or CRYogenic Orbital TEstbed, it will be a testbed for demonstrating a number of technologies needed for cryogenic propellant depots, with several small-scale demonstrations planned for 2012-2014. , ULA says this mission could launch as soon as 2012 if funded. The ULA CRYOTE small-scale demonstrations are intended to lead to a ULA large-scale cryo-sat flagship technology demonstration in 2015. The Future In-Space Operations (FISO) Working Group, a consortium of participants from NASA, industry and academia, discussed propellant depot concepts and plans on several occasions in 2010, with presentations of optimal depot locations for human space exploration beyond low Earth orbit, a proposed simpler (single vehicle) first-generation propellant depot and six important propellant-depot-related technologies for reusable cislunar transportation. NASA also has plans to mature techniques for enabling and enhancing space flights that use propellant depots in the "CRYOGENIC Propellant STorage And Transfer (CRYOSTAT) Mission". The CRYOSTAT vehicle is expected to be launched to LEO in 2015. The CRYOSTAT architecture comprises technologies in the following categories: The "Simple Depot" mission was proposed by NASA in 2011 as a potential first PTSD mission, with launch no earlier than 2015, on an Atlas V 551 | https://en.wikipedia.org/wiki?curid=22202480 |
Propellant depot "Simple Depot" would utilize the "used" (nearly-emptied) Centaur upper stage LH2 tank for long-term storage of LO2 while LH2 will be stored in the Simple Depot LH2 module, which is launched with only ambient-temperature gaseous Helium in it. The SD LH2 tank was to be diameter and long, in volume, and store 5 mT of LH2. "At a useful mixture ratio (MR) of 6:1 this quantity of LH2 can be paired with 25.7 mT of LO2, allowing for 0.7 mT of LH2 to be used for vapor cooling, for a total useful propellant mass of 30 mT. ... the described depot will have a boil-off rate of approaching 0.1 percent per day, consisting entirely of hydrogen." In September 2010, ULA released a "Depot-Based Space Transportation Architecture" concept to propose propellant depots that could be used as way-stations for other spacecraft to stop and refuel—either in low Earth orbit (LEO) for beyond-LEO missions, or at Lagrangian point for interplanetary missions—at the AIAA Space 2010 conference. The concept proposes that waste gaseous hydrogen—an inevitable byproduct of long-term liquid hydrogen storage in the radiative heat environment of space—would be usable as a monopropellant in a solar-thermal propulsion system. The waste hydrogen would be productively utilized for both orbital stationkeeping and attitude control, as well as providing limited propellant and thrust to use for orbital maneuvers to better rendezvous with other spacecraft that would be inbound to receive fuel from the depot | https://en.wikipedia.org/wiki?curid=22202480 |
Propellant depot As part of the Depot-Based Space Transportation Architecture, ULA has proposed the Advanced Common Evolved Stage (ACES) upper stage rocket. ACES hardware is designed from the start as an in-space propellant depot that could be used as way-stations for other rockets to stop and refuel on the way to beyond-LEO or interplanetary missions, and to provide the high-energy technical capacity for the cleanup of space debris. In August 2011, NASA made a significant contractual commitment to the development of propellant depot technology by funding four aerospace companies to "define demonstration missions that would validate the concept of storing cryogenic propellants in space to reduce the need for large launch vehicles for deep-space exploration." These study contracts for storing/transferring cryogenic propellants and cryogenic depots were signed with Analytical Mechanics Associates, Boeing, Lockheed Martin and Ball Aerospace. Each company will receive under the contract. The Chinese Space Agency (CNSA) performed its first satellite-to-satellite on-orbit refueling test in June 2016. There are a number of design issues with propellant depots, as well as several tasks that have not, to date, been tested in space for on-orbit servicing missions. The design issues include propellant settling and transfer, propellant usage for attitude control and reboost, the maturity of the refrigeration equipment/cryocoolers, and the power and mass required for reduced or zero boiloff depots with refrigeration | https://en.wikipedia.org/wiki?curid=22202480 |
Propellant depot Transfer of liquid propellants in microgravity is complicated by the uncertain distribution of liquid and gasses within a tank. Propellant settling at an in-space depot is thus more challenging than in even a slight gravity field. ULA plans to use the DMSP-18 mission to flight-test centrifugal propellant settling as a cryogenic fuel management technique that might be used in future propellant depots. The proposed Simple Depot PTSD mission utilizes several techniques to achieve adequate settling for propellant transfer. In the absence of gravity, propellant transfer is somewhat more difficult, since liquids can float away from the inlet. As part of the Orbital Express mission in 2007, hydrazine propellant was successfully transferred between two single-purpose designed technology demonstration spacecraft. The Boeing servicing spacecraft ASTRO transferred propellant to the Ball Aerospace serviceable client spacecraft NEXTSat. Since no crew were present on either spacecraft, this was reported as the first autonomous spacecraft-to-spacecraft fluid transfer. After propellant has been transferred to a customer the depot's tanks will need refilling. Organizing the construction and launch of the tanker rockets bearing the new fuel is the responsibility of the propellant depot's operator | https://en.wikipedia.org/wiki?curid=22202480 |
Propellant depot Since space agencies like NASA hope to be purchasers rather than owners, possible operators include the aerospace company that constructed the depot, manufacturers of the rockets, a specialist space depot company, or an oil/chemical company that refines the propellant. By using several tanker rockets the tankers can be smaller than the depot and larger than the spacecraft they are intended to resupply. Short range chemical propulsion tugs belonging to the depot may be used to simplify docking tanker rockets and large vehicles like Mars Transfer Vehicles. Transfers of propellant between the LEO depot, reachable by rockets from Earth, and the deep space ones such as the Lagrange Points and Phobos depots can be performed using Solar electric propulsion (SEP) tugs. Two missions are currently under development or proposed to support propellant depot refilling. In addition to refueling and servicing geostationary communications satellites with the fuel that is initially launched with the MDA Space Infrastructure Servicing vehicle, the SIS vehicle is being designed to have the ability to orbitally maneuver to rendezvous with a replacement fuel canister after transferring the of fuel in the launch load, enabling further refueling of additional satellites after the initial multi-satellite servicing mission is complete | https://en.wikipedia.org/wiki?curid=22202480 |
Propellant depot The proposed Simple Depot cryogenic PTSD mission utilizes "remote berthing arm and docking and fluid transfer ports" both for propellant transfer to other vehicles, as well as for refilling the depot up to the full 30 tonne propellant capacity. S.T. Demetriades proposed a method for refilling by collecting atmospheric gases. Moving in low Earth orbit, at an altitude of around 120 km, Demetriades' proposed depot extracts air from the fringes of the atmosphere, compresses and cools it, and extracts liquid oxygen. The remaining nitrogen is used as propellant for a nuclear-powered magnetohydrodynamic engine, which maintains the orbit, compensating for atmospheric drag. This system was called “PROFAC” (PROpulsive Fluid ACcumulator). There are, however, safety concerns with placing a nuclear reactor in low Earth orbit. Demetriades' proposal was further refined by Christopher Jones and others In this proposal, multiple collection vehicles accumulate propellant gases at around 120 km altitude, later transferring them to a higher orbit. However, Jones' proposal does require a network of orbital power-beaming satellites, to avoid placing nuclear reactors in orbit. Asteroids can also be processed to provide liquid oxygen. Propellant depots in LEO are of little use for transfer between two low earth orbits when the depot is in a different orbital plane than the target orbit. The delta-v to make the necessary plane change is typically extremely high | https://en.wikipedia.org/wiki?curid=22202480 |
Propellant depot On the other hand, depots are typically proposed for exploration missions, where the change over time of the depot's orbit can be chosen to align with the departure vector. This allows one well-aligned departure time minimizing fuel use that requires a very precisely-timed departure. Less efficient departure times from the same depot to the same destination exist before and after the well-aligned opportunity, but more research is required to show whether the efficiency falls off quickly or slowly. By contrast, launching directly in only one launch from the ground without orbital refueling or docking with another craft already on orbit offers daily launch opportunities though it requires larger and more expensive launchers. The restrictions on departure windows arise because low earth orbits are susceptible to significant perturbations; even over short periods they are subject to nodal regression and, less importantly, precession of perigee. Equatorial depots are more stable but also more difficult to reach. New approaches have been discovered for LEO to interplanetary orbital transfers where a three-burn orbital transfer is used, which includes a plane change at apogee in a highly-elliptical phasing orbit, in which the incremental delta-v is small—typically less than five percent of the total delta-v—"enabling departures to deep-space destinations [taking] advantage of a depot in LEO" and providing frequent departure opportunities | https://en.wikipedia.org/wiki?curid=22202480 |
Propellant depot More specifically, the 3-burn departure strategy has been shown to enable a single LEO depot in an ISS-inclination orbit (51 degrees) to dispatch nine spacecraft to "nine different interplanetary targets [where the depot need not] perform any phasing maneuvers to align with any of the departure asymptotes ... [including enabling] extending the economic benefits of dedicated smallsat launch to interplanetary missions." Boil-off of cryogenic propellants in space may be mitigated by both technological solutions as well as system-level planning and design. From a technical perspective: for a propellant depot with passive insulation system to effectively store cryogenic fluids, boil-off caused by heating from solar and other sources must be mitigated, eliminated, or used for economic purposes. For non-cryogenic propellants, boil-off is not a significant design problem. Boil off rate is governed by heat leakage and by the quantity of propellant in the tanks. With partially filled tanks, the percentage loss is higher. Heat leakage depends on surface area, while the original mass of propellant in the tanks depends on volume. So by the cube-square law, the smaller the tank, the faster the liquids will boil off. Some propellant tank designs have achieved a liquid hydrogen boil off rate as low as approximately 0.13% per day (3.8% per month) while the much higher temperature cryogenic fluid of liquid oxygen would boil off much less, about 0.016% per day (0.49% per month) | https://en.wikipedia.org/wiki?curid=22202480 |
Propellant depot It is possible to achieve zero boil-off (ZBO) with cryogenic propellant storage using an active thermal control system. Tests conducted at the NASA Lewis Research Center's Supplemental Multilayer Insulation Research Facility (SMIRF) over the summer of 1998 demonstrated that a hybrid thermal control system could eliminate boiloff of cryogenic propellants. The hardware consisted of a pressurized tank insulated with 34 layers of insulation, a condenser, and a Gifford-McMahon (GM) cryocooler that has a cooling capacity of 15 to 17.5 watt (W). Liquid hydrogen was the test fluid. The test tank was installed into a vacuum chamber, simulating space vacuum. In 2001, a cooperative effort by NASA's Ames Research Center, Glenn Research Center, and Marshall Space Flight Center (MSFC) was implemented to develop zero-boiloff concepts for in-space cryogenic storage. Main program element was a large-scale, zero-boiloff demonstration using the MSFC multipurpose hydrogen test bed (MHTB) - 18.10 m3 L tank (about 1300 kg of ). A commercial cryocooler was interfaced with an existing MHTB spray bar mixer and insulation system in a manner that enabled a balance between incoming and extracted thermal energy. Another NASA study in June 2003 for conceptual Mars mission showed mass savings over traditional, passive- only cryogenic storage when mission durations are 5 days in LEO for oxygen, 8.5 days for methane and 64 days for hydrogen. Longer missions equate to greater mass savings | https://en.wikipedia.org/wiki?curid=22202480 |
Propellant depot Cryogenic xenon saves mass over passive storage almost immediately. When power to run the ZBO is already available, the break-even mission durations are even shorter, e.g. about a month for hydrogen. The larger the tank, the fewer days in LEO when ZBO has reduced mass. In addition to technical solutions to the challenge of excessive boil-off of cryogenic rocket propellants, system-level solutions have been proposed. From a systems perspective, reductions in the standby time of the LH2 cryogenic storage in order to achieve, effectively, a just in time (JIT) delivery to each customer, matched with the balanced refinery technology to split the long-term storable feedstock—water—into the stoichiometric LOX/LH2 necessary, is theoretically capable of achieving a system-level solution to boil-off. Such proposals have been suggested as supplementing good technological techniques to reduce boil-off, but would not replace the need for efficient technological storage solutions. United Launch Alliance (ULA) has proposed a cryogenic depot which would use a conical sun shield to protect the cold propellants from solar and Earth radiation. The open end of the cone allows residual heat to radiate to the cold of deep space, while the closed cone layers attenuates the radiative heat from the Sun and Earth. Other issues are hydrogen embrittlement, a process by which some metals (including iron and titanium) become brittle and fracture following exposure to hydrogen | https://en.wikipedia.org/wiki?curid=22202480 |
Propellant depot The resulting leaks makes storing cryogenic propellants in zero gravity conditions difficult. In the early 2010s, several in-space refueling projects got under-way. Two private initiatives and a government-sponsored test mission were in some level of development or testing . The NASA Robotic Refueling Mission was launched in 2011 and successfully completed a series of robotically-actuated propellant transfer experiments on the exposed facility platform of the International Space Station in January 2013. The set of experiments included a number of propellant valves, nozzles and seals similar to those used on many satellites and a series of four prototype tools that could be attached to the distal end of a Space Station robotic arm. Each tool was a prototype of "devices that could be used by future satellite servicing missions to refuel spacecraft in orbit. RRM is the first in-space refueling demonstration using a platform and fuel valve representative of most existing satellites, which were never designed for refueling. Other satellite servicing demos, such as the U.S. military's Orbital Express mission in 2007, transferred propellant between satellites with specially-built pumps and connections." , a small-scale refueling demonstration project for reaction control system (RCS) fluids is under development. Canada-based MDA Corporation announced in early 2010 that they were designing a single spacecraft that would refuel other spacecraft in orbit as a satellite-servicing demonstration | https://en.wikipedia.org/wiki?curid=22202480 |
Propellant depot "The business model, which is still evolving, could ask customers to pay per kilogram of fuel successfully added to their satellite, with the per-kilogram price being a function of the additional revenue the operator can expect to generate from the spacecraft’s extended operational life." The plan is that the fuel-depot vehicle would maneuver to an operational communications satellite, dock at the target satellite's apogee-kick motor, remove a small part of the target spacecraft's thermal protection blanket, connect to a fuel-pressure line and deliver the propellant. "MDA officials estimate the docking maneuver would take the communications satellite out of service for about 20 minutes." , MDA has secured a major customer for the initial demonstration project. Intelsat has agreed to purchase one-half of the propellant payload that the MDA spacecraft would carry into geostationary orbit. Such a purchase would add somewhere between two and four years of additional service life for up to five Intelsat satellites, assuming 200 kg of fuel is delivered to each one. , the spacecraft could be ready to begin refueling communication satellites by 2015. , no customers have signed up for an MDA refueling mission. In 2017, MDA announced that it was restarting its satellite servicing business, with Luxembourg-based satellite owner/operator SES S.A. as its first customer. Competitive design alternatives to in-space RCS fuel transfer exist | https://en.wikipedia.org/wiki?curid=22202480 |
Propellant depot It is possible to bring additional propellant to a space asset, and utilize the propellant for attitude control or orbital velocity change, without ever transferring the propellant to the target space asset. The ViviSat Mission Extension Vehicle, also under development since the early 2010s, illustrates one alternative approach that would connect to the target satellite similarly to MDA SIS, via the kick motor, but will not transfer fuel. Rather, the Mission Extension Vehicle will use "its own thrusters to supply attitude control for the target." ViviSat believes their approach is more simple and can operate at lower cost than the MDA propellant transfer approach, while having the technical ability to dock with and service a greater number (90 percent) of the approximately 450 geostationary satellites in orbit. , no customers have signed up for a ViviSat-enabled mission extension. In 2015, Lockheed Martin proposed the Jupiter space tug. If built, Jupiter would operate in low Earth orbit shuttling cargo carriers to and from the International Space Station, remaining on orbit indefinitely, and refueling itself from subsequent transport ships carrying later cargo carrier modules. In December 2018, Orbit Fab, a silicon valley startup company founded in early 2018, flew the first of a series of experiments to the ISS in order to test and demonstrate technologies to allow for commercial in space refueling. These first rounds of testing utilise water as a propellant simulant. | https://en.wikipedia.org/wiki?curid=22202480 |
Moscow State University of Fine Chemical Technologies named after M.V. Lomonosov (traditional abbreviation "MITHT") is one of the oldest universities in the country that offer training in a wide range of specialties in the field of chemical technology. Currently, there are more than 4,500 students in nine areas of undergraduate, 28 master's programs and 23 scientific specialties for training of candidates and doctors of science. In MITHT there are 8 dissertation councils for doctoral and PhD theses. Research and teaching activities are performed by more than 400 professors and 158 scientists, including more than 120 doctors of science and professors. Located in Moscow at Vernadsky Avenue, Building 86 (new building complex) and Malaya Pirogovskaya, Building 1 (historic building). History of the University and its continuing operations as a higher education institution begins 1 July 1900 and covers several stages. 1 July (14 July, New Style) 1900 was organized the Moscow Higher Women Courses (MHWC). Their structure originally consisted of two departments: History and Philosophy and Physics and Mathematics. On the last one were soon opened two offices: mathematical and natural, and after a few years two more – medical and chemical-pharmaceutical. The initiators and the first lecturers were outstanding scientists, academics subsequently S. A. Chaplygin, V. I. Vernadsky, N. D. Zelinsky (the inventor of the gas mask (1916)), Professors V. F. Davidov, B. K. Mlodzeevskii, A. N. Reformatsky, A. A. Eichenwald, S. G. Krapivin. The first director of MHWC was Professor V. I | https://en.wikipedia.org/wiki?curid=22208238 |
Moscow State University of Fine Chemical Technologies Guerrier. In 1905 as a director was elected S. A. Chaplygin, the leading scientist in the field of hydro- and aerodynamics, the organizer of the construction of school buildings on the Malaya Pirogovskaya street (formerly Devichie Pole). He remained in that post until 1918. By the beginning of World War I MHWC turned into the one of the largest higher education institutions in the country. The number of trainees reached 710, and during the existence of courses released 5760 professionals. In turning into a first-class university MHWC paramount importance had an exceptional organizational skill of S. A. Chaplygin, later shown to them with equal brilliance in creating TsAGI. 16 October 1918 MHWC were converted into second Moscow State University. The first rector of the 2nd Moscow State University was appointed academician S. S. Nametkin who worked since 1913 as a head of the Department of Organic Chemistry of MHWC. As rector, he remained until 1924. As part of the 2nd Moscow State University became the chemical-pharmaceutical department, which in 1919 was transformed into the chemical and pharmaceutical department. At this time, on the faculty worked well-known Professors A. M. Berkengeim, B. K. Mlodzeevskii, S. S. Nametkin, M. I. Prozin, A. N. Reformatsky, O. N. Tsuberbiller. In 1929, the faculty became a chemical faculty of the university type with specialties such as: Faculty graduates go to work in the factories, involve in the implementation of research projects that receive a wide scope | https://en.wikipedia.org/wiki?curid=22208238 |
Moscow State University of Fine Chemical Technologies During 1922 – 1928 years it has been published about 300 papers and 11 monographs. The greatest successes are achieved in the fields of organic and pharmaceutical chemistry under the direction of heads of departments, academics S. S. Nametkin, B. M. Rodionov, Professor A. M. Berkengeim. Production of new drugs being introduced in the pharmaceutical factory belonging to faculty. 18 April 1930 by order of the People's Commissariat second MSU was reorganized into three independent institutions: Medical (now RSMU them. Pirogov) Pedagogical (now MPSU), and Chemical Technology (now MITHT). Last transferred to the jurisdiction of the Vsehimprom VSNKh USSR. In addressing this issue directly involved Sergo Ordzhonikidze. 10 May 1931 Chemical and Pharmaceutical Faculty became an independent and received a new name – the Moscow Institute of Fine Chemical Technology (MITHT). Historically, the name of the Institute is due to the nature of objects that are studied by students: they were small capacity chemical and pharmaceutical technology, technology of platinum group metals and rare-earth elements. From this moment begins a new stage of development of the institution, which is quickly becoming one of the leading universities in the chemical industry. Front of it set the goal of training for high-tech industries of chemical technology | https://en.wikipedia.org/wiki?curid=22208238 |
Moscow State University of Fine Chemical Technologies In MITHT the first time in the country began to train engineers on the technology of thin inorganic products, synthetic rubber, thin organic produce synthetic liquid fuels, organometallic compounds and a number of other specialties. In the process of restructuring of education at the institute have been preserved and developed the best traditions of MHWC and 2nd Moscow State University: a high level of theoretical training and a combination of academic and scientific work, helped by the fact that the teaching work at the institute and chairing of departments were performed by outstanding scientists and educators which created a school and research areas. Special departments were prepared engineers for industries which were still being created in the first five years. At the time, were of great importance establishment of a domestic pharmaceutical industry and the country's liberation on imports of medicines. Were developed and implemented methods of production of such drugs as atophan, benzocaine, procaine, bromural, thiokol, ichtyol, validol, antipyrine, caffeine, alkaloids and others. In 1938, in MITHT under the leadership of academic A. N. Nesmeyanov (later President of the RAS) began work in the field of organometallic compounds. Also, the Institute prepared professionals for the companies producing such important national defense materials, such as tungsten, molybdenum, vanadium, and rare-earth elements. So, Professor I. Ya. Bashilov created the production technology of uranium and radium | https://en.wikipedia.org/wiki?curid=22208238 |
Moscow State University of Fine Chemical Technologies And under the guidance of Professor G. A. Meyerson were carried out important work on carbothermy and getting super-hard alloys. 7 May 1940 for academic achievement and great progress in the preparation of chemists institute is named after the outstanding Russian scientist Mikhail Vasilievich Lomonosov. During the war, groups of departments in collaboration with industry and research institutes conduct intensive research on defense-related development and implementation of the executed work. Thus, under the supervision of Professor N. I. Gelperin was created the most powerful bomb in World War II – FAB-5000NG that terrified Hitlerites. Efforts of the Institute as a whole and individual professors and teachers were appreciated by the country. Professors B. A. Dogadkin, N. I. Krasnopevtsev, V. V. Lebedinskij, S. S. Medvedev, S. I. Sklyarenko and Ya. K. Sirkin were awarded the Stalin Prize laureates, and associate professor K. A. Bolshakov won that title twice. The post-war period was characterized by intensive work of the Institute staff in the aftermath of the war, the creation of the necessary conditions for teaching and research. Among the most important achievements of the postwar period MITHT need to include: The high scientific – technical research conducted at the institute, evidenced by the fact that MITHT became one of the first places among the universities and research institutes on the number of implemented inventions | https://en.wikipedia.org/wiki?curid=22208238 |
Moscow State University of Fine Chemical Technologies Employees of the institute published 450–500 scientific papers and received 50–60 invention certificates a year. The Institute conducts research on economic agreements and contracts on cooperation with industry and research institutes, whose number exceeded 150. MITHT, in fact, has turned into a complex of the university and research institutes. On 2500–3000 students, in addition to 400 professors and lecturers, employed more than 900 scientists. Two to one – that is the ratio of students, academic and teaching staff, which was reached in MITHT. Good specialist, engineer cannot be prepared without bringing him to participate in real, serious scientific research in the learning process. 11 February 1971 for his services to the training of specialists for the national economy and the development of scientific research institute was awarded the Order of the Red Banner of Labour. Education in MITHT always featured a deep fundamental training, which included, along with a full range of natural sciences study the big cycle engineering and technological disciplines. Special training was carried out by the so-called "thin" chemical technologies that are, as a rule, small capacity technology, implemented on the basis of the latest achievements of chemical science and technology. That is, in fact, the students received a university degree in combination with engineering training. In 1992, the Moscow Institute of Fine Chemical Technology named after M. V | https://en.wikipedia.org/wiki?curid=22208238 |
Moscow State University of Fine Chemical Technologies Lomonosov has received a new, higher educational status – status of the Academy. With the name change has changed the status and range of activities of the institute along with old technology, new specialty Humanitarian – Management Profile: "Economics and Management (chemical industry)", "Environmental Protection", "Standardization and Certification". These specialties are subject to major technologies and solve their narrow-profile tasks. Before the transition to a tiered structure the education of students was carried out in one direction, "Chemical Technology and Biotechnology", which consists of seven specialties. After the transition academy led training in seven areas of undergraduate, graduate five areas (including 26 master's programs) and 13 majors (including 25 majors) in full-time and part-correspondence courses, and conducted post-graduate education in 24 specialties and additional education in primary educational programs MITHT. To implement in MITHT a tiered system of higher education were opened new training units. Along with main faculties teaching of students was performed at the Faculty of Natural Science, Faculty of Humanities, Faculty of Management, Economics and Environment, Faculty of Engineering, Faculty of further education at the Institute of Distance Education | https://en.wikipedia.org/wiki?curid=22208238 |
Moscow State University of Fine Chemical Technologies According to the Federal Agency for Supervision in Education and Science in 2008 in MITHT worked one of the most highly qualified scientific and technical teaching staff of universities and academies of Russia: doctors and candidates of sciences accounted for about 80% of the teachers. At the academy a total enrollment of 4,500 undergraduate and graduate students, taught 119 professors, doctors, and 218 associate professors, candidates of sciences. In 2011, the Academy received a University status. The successes of the University in education, research and innovation, the recognition of the scientific and pedagogical schools, its international status and worldwide fame are undoubtedly merit in the first professors, assistant professors, lecturers, and they have created in the walls of the university unique creative scientific and educational environment. Friendly and supportive atmosphere of the business and human interaction with the students and teachers together form the necessary conditions for the development of the individual, focused, motivated professional growth. Chemistry: Chemical technology: Biotechnology: Materials science and technology of materials: Technosphere Safety: Standardization and Certification: | https://en.wikipedia.org/wiki?curid=22208238 |
Catabolite repression Carbon catabolite repression, or simply catabolite repression, is an important part of global control system of various bacteria and other micro-organisms. allows micro-organisms to adapt quickly to a preferred (rapidly metabolisable) carbon and energy source first. This is usually achieved through inhibition of synthesis of enzymes involved in catabolism of carbon sources other than the preferred one. The catabolite repression was first shown to be initiated by glucose and therefore sometimes referred to as the glucose effect. However, the term "glucose effect" is actually a misnomer since other carbon sources are known to induce catabolite repression. was extensively studied in "Escherichia coli". "E. coli" grows faster on glucose than on any other carbon source. For example, if "E. coli" is placed on an agar plate containing only glucose and lactose, the bacteria will use glucose first and lactose second. When glucose is available in the environment, the synthesis of β-galactosidase is under repression due to the effect of catabolite repression caused by glucose. The catabolite repression in this case is achieved through the utilization of phosphotransferase system. An important enzyme from the phosphotransferase system called Enzyme II A (EIIA) plays a central role in this mechanism. There are different catabolite-specific EIIA in a single cell, even though different bacterial groups have specificities to different sets of catabolites | https://en.wikipedia.org/wiki?curid=22215454 |
Catabolite repression In enteric bacteria one of the EIIA enzymes in their set is specific for glucose transport only. When glucose levels are high inside the bacteria, EIIA mostly exists in its unphosphorylated form. This leads to inhibition of adenylyl cyclase and lactose permease, therefore cAMP levels are low and lactose can not be transported inside the bacteria. Once the glucose is all used up, the second preferred carbon source (i.e. lactose) has to be used by bacteria. Absence of glucose will "turn off" catabolite repression. When glucose levels are low, the phosphorylated form of EIIA accumulates and consequently activates the enzyme adenylyl cyclase, which will produce high levels of cAMP. cAMP binds to catabolite activator protein (CAP) and together they will bind to a promoter sequence on the lac operon. However, this is not enough for the lactose genes to be transcribed. Lactose must be present inside the cell to remove the lactose repressor from the operator sequence (transcriptional regulation). When these two conditions are satisfied, it means for the bacteria that glucose is absent and lactose is available. Next, bacteria start to transcribe the lac operon and produce β-galactosidase enzymes for lactose metabolism. The example above is a simplification of a complex process. is considered to be a part of global control system and therefore it affects more genes rather than just lactose gene transcription | https://en.wikipedia.org/wiki?curid=22215454 |
Catabolite repression Gram positive bacteria such as "Bacillus subtilis" have a cAMP-independent catabolite repression mechanism controlled by catabolite control protein A (CcpA). In this alternative pathway CcpA negatively represses other sugar operons so they are off in the presence of glucose. It works by the fact that Hpr is phosphorylated by a specific mechanism, when glucose enters through the cell membrane protein EIIC, and when Hpr is phosphoralated it can then allow CcpA to block transcription of the alternative sugar pathway operons at their respective cre sequence binding sites. Note that "E. coli" has a similar cAMP-independent catabolite repression mechanism that utilizes a protein called catabolite repressor activator (Cra). | https://en.wikipedia.org/wiki?curid=22215454 |
Clarification and stabilization of wine In winemaking, clarification and stabilization are the processes by which insoluble matter suspended in the wine is removed before bottling. This matter may include dead yeast cells (lees), bacteria, tartrates, proteins, pectins, various tannins and other phenolic compounds, as well as pieces of grape skin, pulp, stems and gums. Clarification and stabilization may involve fining, filtration, centrifugation, flotation, refrigeration, pasteurization, and/or barrel maturation and racking. In wine tasting, a wine is considered "clear" when there are no visible particles suspended in the liquid and, especially in the case of white wines, when there is some degree of transparency. A wine with too much suspended matter will appear cloudy and dull, even if its aroma and flavor are unaffected; wines therefore generally undergo some kind of clarification. Before fermentation, pectin-splitting enzymes and, for white wine, fining agents such as bentonite may be added to the must in order to promote the eventual agglomeration and settling of colloids. Pectins are structural molecules in the cell walls of fruits which have the important function of 'gumming' plant cells together. The pectin content of grapes increases steadily throughout ripening, reaching levels of about 1 g/l, although it varies by varietal and pre-fermentation handling processes. Large pectin molecules can affect the amount of juice yielded at pressing, ease of filtration and clarification, and extraction of tannins | https://en.wikipedia.org/wiki?curid=22216378 |
Clarification and stabilization of wine Grapes contain natural pectolytic enzymes responsible for softening the grape berries during ripening, but these are not active under wine-making conditions (due to pH level, SO, and alcohol.) Therefore, fungal pectolytic enzymes are often added to white must to break up pectins, decrease the viscosity of the juice, and speed up settling. In red musts, this increases color and tannin extraction. After fermentation, the force of gravity may eventually cause the wine to "fall bright" or clarify naturally, as the larger suspended particles gradually settle to the bottom of the storage vessel. The wine can then be siphoned or "racked" off the compact solids into a new container. But this process may take many months, or even years, as well as several rackings, in order to produce a perfectly clear wine. Producers can accelerate the process by using fining agents, filtration and/or flotation. In winemaking, fining is the process where a substance (fining agent) is added to the wine to create an adsorbent, enzymatic or ionic bond with the suspended particles, producing larger molecules and larger particles that will precipitate out of the wine more readily and rapidly. Unlike filtration, which can only remove particulates (such as dead yeast cells and grape fragments), fining can remove soluble substances such as polymerized tannins, coloring phenols and proteins; some of these proteins can cause haziness in wines exposed to high temperatures after bottling | https://en.wikipedia.org/wiki?curid=22216378 |
Clarification and stabilization of wine The reduction of tannin can reduce astringency in red wines intended for early drinking. Many substances have historically been used as fining agents, including dried blood powder. Today, there are two general types of fining agents — organic compounds and solid/mineral materials. Organic compounds used as fining agents are generally animal based, a possible cause of concern to vegans. The most common organic compounds used include egg whites, casein derived from milk, gelatin and isinglass obtained from the bladders of fish. Pulverized minerals and solid materials can also be used, with bentonite clay being one of the most common, thanks to its effectiveness in absorbing proteins and some bacteria. Activated carbon from charcoal is used to remove some phenols that contribute to browning as well as some particles that produce "off-odors" in the wine. In a process known as blue fining, potassium ferrocyanide is sometimes used to remove any copper and iron particles that have entered the wine from bentonite, metal winery and vineyard equipment, or vineyard sprays such as Bordeaux mixture. Because potassium ferrocyanide may form hydrogen cyanide its use is highly regulated and, in many wine producing countries, illegal. Silica and kaolin are also sometimes used. Some countries, such as Australia and New Zealand, have wine labeling laws that require the use of fining agents that may be an allergenic substance to appear on the wine label | https://en.wikipedia.org/wiki?curid=22216378 |
Clarification and stabilization of wine A study conducted by the University of California, Davis Department of Viticulture and Enology, however, found that no detectable amount of inorganic fining agents, and only trace quantities of proteinaceous agents, are left in the wine. There is the risk of valuable aromatic molecules being precipitated out along with the less desirable matter. Some producers of premium wine avoid fining, or delay it in order to leach more flavor and aroma from the phenols before they are removed. While fining clarifies wine by binding to suspended particles and precipitating out as larger particles, filtration works by passing the wine through a filter medium that captures particles larger than the medium's holes. Complete filtration may require a series of filtering through progressively finer filters. Many white wines require the removal of all potentially active yeast and/or lactic acid bacteria if they are to remain reliably stable in bottle, and this is usually now achieved by fine filtration. Most filtration in a winery can be classified as either the coarser depth filtration or the finer surface filtration. In depth filtration, often done after fermentation, the wine is pushed through a thick layer of pads made from cellulose fibers, diatomaceous earth, or perlite. In surface filtration, the wine passes through a thin membrane. Running the wine parallel to the filter surface, known as cross-flow filtration, will minimize the filter clogging | https://en.wikipedia.org/wiki?curid=22216378 |
Clarification and stabilization of wine The finest surface filtration, microfiltration, can sterilize the wine by trapping all yeast and, optionally, bacteria, and so is often done immediately prior to bottling. An absolute rated filter of 0.45 µm is generally considered to result in a microbially stable wine and is accomplished by the use of membrane cartridges, most commonly polyvinylidene fluoride (PVDF). Certain red wines may be filtered to 0.65 µm, to remove yeast, or to 1.0 µm to remove viable brettanomyces only. The winemaking technique of flotation was adapted from the froth flotation process used in the mining industry for ore refining. In this process, small bubbles of air (or compressed nitrogen) are injected into the bottom of a tank. As the bubbles rise through the must, grape solids, including phenolic compounds prone to oxidation and browning, will tend to cling to the bubbles, creating a froth that can be removed from the wine. This must be done prior to fermentation, since yeast will inhibit the flocculation involved. As a complex chemical mixture dependent on the activity of microorganisms, wine can be unstable and reactive to changes in its environment. Once bottled, a wine may be exposed to extremes of temperature and humidity, as well as violent movement during transportation and storage. These may cause cloudiness, sedimentation and/or the formation of tartrate crystals; more seriously, they may also cause spoilage or the production of carbonic gas | https://en.wikipedia.org/wiki?curid=22216378 |
Clarification and stabilization of wine Tartaric acid is the most prominent acid in wine with the majority of the concentration present as potassium bitartrate. During fermentation, these tartrates bind with the lees, pulp debris and precipitated tannins and pigments. While there is some variation according to grape variety and climate, usually about half of the deposits are soluble in the wine, but on exposure to low temperature they may crystallize out unpredictably. The crystals, though harmless, may be mistaken for broken glass, or simply reckoned unattractive by consumers. To prevent this the wine may undergo "cold stabilization", in which it is cooled to near its freezing point to provoke crystallization before bottling. In some white wines there are significant quantities of proteins that, being "heat-unstable", will coagulate if exposed to excessively fluctuating heat; the use of fining agents such as bentonite can prevent the haze this causes. A wine that has not been sterilized by filtration might well still contain live yeast cells and bacteria. If both alcoholic and malolactic fermentation have run to completion, and neither excessive oxygen nor "Brettanomyces" yeast are present, this ought to cause no problems; modern hygiene has largely eliminated spoilage by bacteria such as acetobacter, which turns wine into vinegar. If there is residual sugar, however, it may undergo secondary fermentation, creating dissolved carbon dioxide as a by-product. When the wine is opened, it will be spritzy or "sparkling" | https://en.wikipedia.org/wiki?curid=22216378 |
Clarification and stabilization of wine In a wine intended to be still this is regarded as a serious fault; it can even cause the bottle to explode. Similarly, a wine that has not been put through complete malolactic fermentation may undergo it in bottle, reducing its acidity, generating carbon dioxide, and adding a diacetyl butterscotch aroma. "Brettanomyces" yeasts add 4-ethylphenol, 4-ethylguaiacol and isovaleric acid horse-sweat aromas. These phenomena may be prevented by sterile filtration, by the addition of relatively large quantities of sulfur dioxide and sometimes sorbic acid, by mixing in alcoholic spirit to give a fortified wine of sufficient strength to kill all yeast and bacteria, or by pasteurization. Pasteurization gives a kosher wine of the type called "mevushal", literally "cooked" or "boiled", that can be handled by non-Jews and non-observant Jews without losing its kosher status. Typically, the wine is heated to 185°F (85°C) for a minute, then cooled to 122°F (50°C), at which temperature it remains for up to three days, killing all yeast and bacteria. It may then be allowed to cool, or be bottled "hot" and cooled by water sprays. Since pasteurization affects a wine's flavor and aging potential it is not used for premium wines. A gentler procedure known as flash pasteurization involves heating to 205°F (95°C) for a few seconds, followed by rapid cooling. Clarification tends to stabilize wine, since it removes some of the same particles that promote instability | https://en.wikipedia.org/wiki?curid=22216378 |
Clarification and stabilization of wine The gradual oxidation that occurs during barrel aging also has a naturally stabilizing effect. Some producers prefer not to thoroughly clarify and stabilize their wines, believing that the processes involved may diminish a wine's aroma, flavor, texture, color or aging potential. Wine experts such as Tom Stevenson note that they may improve wine quality when used with moderation and care, or diminish it when used to excess. Winemakers deliberately leave more tartrates and phenolics in wines designed for long aging in bottle so that they are able to develop the aromatic compounds that constitute bouquet. The consumers of some wines, such as red Bordeaux and Port, may expect to see tartrates and sediment after aging in bottle. | https://en.wikipedia.org/wiki?curid=22216378 |
Nucleic acid structure determination Experimental approaches of determining the structure of nucleic acids, such as RNA and DNA, can be largely classified into biophysical and biochemical methods. Biophysical methods use the fundamental physical properties of molecules for structure determination, including X-ray crystallography, NMR and cryo-EM. Biochemical methods exploit the chemical properties of nucleic acids using specific reagents and conditions to assay the structure of nucleic acids. Such methods may involve chemical probing with specific reagents, or rely on native or analogue chemistry. Different experimental approaches have unique merits and are suitable for different experimental purposes. X-ray crystallography is not common for nucleic acids alone, since neither DNA nor RNA readily form crystals. This is due to the greater degree of intrinsic disorder and dynamism in nucleic acid structures and the negatively charged (deoxy)ribose-phosphate backbones, which repel each other in close proximity. Therefore, crystallized nucleic acids tend to be complexed with a protein of interest to provide structural order and neutralize the negative charge. Nucleic acid NMR is the use of NMR spectroscopy to obtain information about the structure and dynamics of nucleic acid molecules, such as DNA or RNA. As of 2003, nearly half of all known RNA structures had been determined by NMR spectroscopy. Nucleic acid NMR uses similar techniques as protein NMR, but has several differences | https://en.wikipedia.org/wiki?curid=22217265 |
Nucleic acid structure determination Nucleic acids have a smaller percentage of hydrogen atoms, which are the atoms usually observed in NMR, and because nucleic acid double helices are stiff and roughly linear, they do not fold back on themselves to give "long-range" correlations. The types of NMR usually done with nucleic acids are H or proton NMR, C NMR, N NMR, and P NMR. Two-dimensional NMR methods are almost always used, such as correlation spectroscopy (COSY) and total coherence transfer spectroscopy (TOCSY) to detect through-bond nuclear couplings, and nuclear Overhauser effect spectroscopy (NOESY) to detect couplings between nuclei that are close to each other in space. Parameters taken from the spectrum, mainly NOESY cross-peaks and coupling constants, can be used to determine local structural features such as glycosidic bond angles, dihedral angles (using the Karplus equation), and sugar pucker conformations. For large-scale structure, these local parameters must be supplemented with other structural assumptions or models, because errors add up as the double helix is traversed, and unlike with proteins, the double helix does not have a compact interior and does not fold back upon itself. NMR is also useful for investigating nonstandard geometries such as bent helices, non-Watson–Crick basepairing, and coaxial stacking. It has been especially useful in probing the structure of natural RNA oligonucleotides, which tend to adopt complex conformations such as stem-loops and pseudoknots | https://en.wikipedia.org/wiki?curid=22217265 |
Nucleic acid structure determination NMR is also useful for probing the binding of nucleic acid molecules to other molecules, such as proteins or drugs, by seeing which resonances are shifted upon binding of the other molecule. Cryogenic electron microscopy (cryo-EM) is a technique that uses an electron beam to image samples that have been cryogenically preserved in an aqueous solution. Liquid samples are pipetted on small metallic grids and plunged into a liquid ethane/propane solution which is kept extremely cold by a liquid nitrogen bath. Upon this freezing process, water molecules in the sample do not have enough time to form hexagonal lattices as found in ice, and therefore the sample is preserved in a glassy water-like state (also referred to as a vitrified ice), making these samples easier to image using the electron beam. An advantage of cryo-EM over x-ray crystallography is that the samples are preserved in their aqueous solution state and not perturbed by forming a crystal of the sample. One disadvantage, is that it is difficult to resolve nucleic acid or protein structures that are smaller than ~75 kilodaltons, partly due to the difficulty of having enough contrast to locate particles in this vitrified aqueous solution. Another disadvantage is that to attain atomic-level structure information about a sample requires taking many images (often referred to as electron micrographs) and averaging over those images in a process called single-particle reconstruction. This is a computationally intensive process | https://en.wikipedia.org/wiki?curid=22217265 |
Nucleic acid structure determination Cryo-EM is a newer, less perturbative version of transmission electron microscopy (TEM). It is less perturbative because the sample is not dried onto a surface, this drying process is often done in negative-stain TEM, and because Cryo-EM does not require contrast agent like heavy metal salts (e.g. uranyl acetate or phoshotungstic acid) which also may affect the structure of the biomolecule. Transmission electron microscopy, as a technique, utilizes the fact that samples interact with a beam of electrons and only parts of the sample that do not interact with the electron beam are allowed to 'transmit' onto the electron detection system. TEM, in general, has been a useful technique in determining nucleic acid structure since the 1960s.. While double-stranded DNA (dsDNA) structure may not traditionally be considered structure, in the typical sense of alternating segments of single- and double-stranded regions, in reality, dsDNA is not simply a perfectly ordered double helix at every location of its length due to thermal fluctuations in the DNA and alternative structures that can form like g-quadruplexes. CryoEM of nucleic acid has been done on ribosomes , viral RNA , and single-stranded RNA structures within viruses. These studies have resolved structural features at different resolutions from the nucleobase level (2-3 angstroms) up to tertiary structure motifs (greater than a nanometer). RNA chemical probing uses chemicals that react with RNAs. Importantly, their reactivity depends on local RNA structure e.g | https://en.wikipedia.org/wiki?curid=22217265 |
Nucleic acid structure determination base-pairing or accessibility. Differences in reactivity can therefore serve as a footprint of structure along the sequence. Different reagents react at different positions on the RNA structure, and have different spectra of reactivity. Recent advances allow the simultaneous study of the structure of many RNAs (transcriptome-wide probing) and the direct assay of RNA molecules in their cellular environment (in-cell probing). Structured RNA is first reacted with the probing reagents for a given incubation time. These reagents would form a covalent adduct on the RNA at the site of reaction. When the RNA is reverse transcribed using a reverse transcriptase into a DNA copy, the DNA generated is truncated at the positions of reaction because the enzyme is blocked by the adducts. The collection of DNA molecules of various truncated lengths therefore informs the frequency of reaction at every base position, which reflects the structure profile along the RNA. This is traditionally assayed by running the DNA on a gel, and the intensity of bands inform the frequency of observing a truncation at each position. Recent approaches use high-throughput sequencing to achieve the same purpose with greater throughput and sensitivity. The reactivity profile can be used to study the degree of structure at particular positions for specific hypotheses, or used in conjunction with computational algorithms to produce a complete experimentally supported structure model. Depending on the chemical reagent used, some reagents, e.g | https://en.wikipedia.org/wiki?curid=22217265 |
Nucleic acid structure determination hydroxyl radicals, would cleave the RNA molecule instead. The result in the truncated DNA is the same. Some reagents, e.g. DMS, sometimes do not block the reverse transcriptase, but trigger a mistake at the site in the DNA copy instead. These can be detected when using high-throughput sequencing methods, and is sometimes employed for improved results of probing as mutational profiling (MaP). Positions on the RNA can be protected from the reagents not only by local structure but also by a binding protein over that position. This has led some work to use chemical probing to also assay protein-binding. As hydroxyl radicals are short-lived in solution, they need to be generated upon experiment. This can be done using HO, ascorbic acid, and Fe(II)-EDTA complex. These reagents form a system that generates hydroxyl radicals through Fenton chemistry. The hydroxyl radicals can then react with the nucleic acid molecules. Hydroxyl radicals attack the ribose/deoxyribose ring and this results in breaking of the sugar-phosphate backbone. Sites under protection from binding proteins or RNA tertiary structure would be cleaved by hydroxyl radical at a lower rate. These positions would therefore show up as absence of bands on the gel, or low signal through sequencing. Dimethyl sulfate, known as DMS, is a chemical that can be used to modify nucleic acids in order to determine secondary structure. Reaction with DMS adds a methyl adduct at the site, known as methylation | https://en.wikipedia.org/wiki?curid=22217265 |
Nucleic acid structure determination In particular, DMS methylates N1 of adenine (A) and N3 of cytosine (C), both located at the site of natural hydrogen bonds upon base-pairing. Therefore, modification can only occur at A and C nucleobases that are single-stranded, base paired at the end of a helix, or in a base pair at or next to a GU wobble pair, the latter two being positions where the base-pairing can occasionally open up. Moreover, since modified sites cannot be base-paired, modification sites can be detected by RT-PCR, where the reverse transcriptase falls off at methylated bases and produces different truncated cDNAs. These truncated cDNAs can be identified through gel electrophoresis or high-throughput sequencing. Improving upon truncation-based methods, DMS mutational profiling with sequencing (DMS-MaPseq) can detect multiple DMS modifications in a single RNA molecule, which enables one to obtain more information per read (for a read of 150 nt, typically two to three mutation sites, rather than zero to one truncation sites), determine structures of low-abundance RNAs, and identify subpopulations of RNAs with alternative secondary structures. DMS-MaPseq uses a thermostable group II intron reverse transcriptase (TGIRT) that creates a mutation (rather than a truncation) in the cDNA when it encounters a base methylated by DMS, but otherwise it reverse transcribes with high fidelity. Sequencing the resulting cDNA identifies which bases were mutated during reverse transcription; these bases cannot have been base-paired in the original RNA | https://en.wikipedia.org/wiki?curid=22217265 |
Nucleic acid structure determination DMS modification can also be used for DNA, for example in footprinting DNA-protein interactions. Selective 2′-hydroxyl acylation analyzed by primer extension, or SHAPE, takes advantage of reagents that preferentially modify the backbone of RNA in structurally flexible regions. Reagents such as N-methylisatoic anhydride (NMIA) and 1-methyl-7-nitroisatoic anhydride (1M7) react with the 2'-hydroxyl group to form adducts on the 2'-hydroxyl of the RNA backbone. Compared to the chemicals used in other RNA probing techniques, these reagents have the advantage of being largely unbiased to base identity, while remaining very sensitive to conformational dynamics. Nucleotides which are constrained (usually by base-pairing) show less adduct formation than nucleotides which are unpaired. Adduct formation is quantified for each nucleotide in a given RNA by extension of a complementary DNA primer with reverse transcriptase and comparison of the resulting fragments with those from an unmodified control. SHAPE therefore reports on RNA structure at the individual nucleotide level. This data can be used as input to generate highly accurate secondary structure models. SHAPE has been used to analyze diverse RNA structures, including that of an entire HIV-1 genome. The best approach is to use a combination of chemical probing reagents and experimental data. In SHAPE-Seq SHAPE is extended by bar-code based multiplexing combined with RNA-Seq and can be performed in a high-throughput fashion | https://en.wikipedia.org/wiki?curid=22217265 |
Nucleic acid structure determination The carbodiimide moiety can also form covalent adducts at exposed nucleobases, which are uracil, and to a smaller extent guanine, upon nucleophilic attack by a deprotonated N. They react primarily with N3 of uracil and N1 of guanine modifying two sites responsible for hydrogen bonding on the bases. 1-cyclohexyl-(2-morpholinoethyl)carbodiimide metho-"p"-toluene sulfonate, also known as CMCT or CMC, is the most commonly used carbodiimide for RNA structure probing. Similar to DMS, it can be detected by reverse transcription followed by gel electrophoresis or high-throughput sequencing. As it is reactive towards G and U, it can be used to complement the data from DMS probing experiments, which inform A and C. 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, also known as EDC, is a water-soluble carbodiimide that exhibits similar reactivity as CMC, and is also used for the chemical probing of RNA structure. EDC is able to permeate into cells and is thus used for direct in-cell probing of RNA in their native environments. Some 1,2-dicarbonyl compounds are able to react with single-stranded guanine (G) at N1 and N2, forming a five-membered ring adduct at the Watson-Crick face. 1,1-Dihydroxy-3-ethoxy-2-butanone, also known as kethoxal, has a structure related to 1,2-dicarbonyls, and was the first in this category used extensively for the chemical probing of RNA. Kethoxal causes the modification of guanine, specifically altering the N1 and the exocyclic amino group (N2) simultaneously by covalent interaction | https://en.wikipedia.org/wiki?curid=22217265 |
Nucleic acid structure determination Glyoxal, methylglyoxal, and phenylglyoxal, which all carry the key 1,2-dicarbonyl moiety, all react with free guanines similar to kethoxal, and can be used to probe unpaired guanine bases in structured RNA. Due to their chemical properties, these reagents can permeated readily into cells and can therefore be used to assay RNAs in their native cellular environments. Light-Activated Structural Examination of RNA (LASER) probing utilizes UV light to activate nicotinoyl azide (NAz), generating highly reactive nitrenium cation in water, which reacts with solvent accessible guanosine and adenosine of RNA at C-8 position through a barrierless Friedel-Crafts reaction. LASER probing targets both single-stranded and double-stranded residues as long as they are solvent accessible. Because hydroxyl radical probing requires synchrotron radiation to measure solvent accessibility of RNA "in vivo", it is hard to apply hydroxyl radical probing to footprint RNA in cells for many laboratories. In contrast, LASER probing utilizes a hand-held UV lamp (20 W) for excitation, it is much easier to apply LASER probing for "in vivo" studying RNA solvent accessibility. This chemical probing method is light-controllable, and probes solvent accessibility of nucleobase, which has been shown to footprint RNA binding proteins inside cells. In-line probing does not involve treatment with any type of chemical or reagent to modify RNA structures | https://en.wikipedia.org/wiki?curid=22217265 |
Nucleic acid structure determination This type of probing assay uses the structure dependent cleavage of RNA; single stranded regions are more flexible and unstable and will degrade over time. The process of in-line probing is often used to determine changes in structure due to ligand binding. Binding of a ligand can result in different cleavage patterns. The process of in-line probing involves incubation of structural or functional RNAs over a long period of time. This period can be several days, but varies in each experiment. The incubated products are then run on a gel to visualize the bands. This experiment is often done using two different conditions: 1) with ligand and 2) in the absence of ligand. Cleavage results in shorter band lengths and is indicative of areas that are not basepaired, as basepaired regions tend to be less sensitive to spontaneous cleavage. In-line probing is a functional assay that can be used to determine structural changes in RNA in response to ligand binding. It can directly show the change in flexibility and binding of regions of RNA in response to a ligand, as well as compare that response to analogous ligands. This assay is commonly used in dynamic studies, specifically when examining riboswitches. Nucleotide analog interference mapping (NAIM) is the process of using nucleotide analogs, molecules that are similar in some ways to nucleotides but lack function, to determine the importance of a functional group at each location of an RNA molecule | https://en.wikipedia.org/wiki?curid=22217265 |
Nucleic acid structure determination The process of NAIM is to insert a single nucleotide analog into a unique site. This can be done by transcribing a short RNA using T7 RNA polymerase, then synthesizing a short oligonucleotide containing the analog in a specific position, then ligating them together on the DNA template using a ligase. The nucleotide analogs are tagged with a phosphorothioate, the active members of the RNA population are then distinguished from the inactive members, the inactive members then have the phosphorothioate tag removed and the analog sites are identified using gel electrophoresis and autoradiography. This indicates a functionally important nucleotide, as cleavage of the phosphorothioate by iodine results in an RNA that is cleaved at the site of the nucleotide analog insert. By running these truncated RNA molecules on a gel, the nucleotide of interest can be identified against a sequencing experiment Site directed incorporation results indicate positions of importance where when running on a gel, functional RNAs that have the analog incorporated at that position will have a band present, but if the analog results in non-functionality, when the functional RNA molecules are run on a gel there will be no band corresponding to that position on the gel | https://en.wikipedia.org/wiki?curid=22217265 |
Nucleic acid structure determination This process can be used to evaluate an entire area, where analogs are placed in site specific locations, differing by a single nucleotide, then when functional RNAs are isolated and run on a gel, all areas where bands are produced indicate non-essential nucleotides, but areas where bands are absent from the functional RNA indicate that inserting a nucleotide analog in that position caused the RNA molecule to become non-functional | https://en.wikipedia.org/wiki?curid=22217265 |
Robert H. Brill Dr Robert Brill is in the field of archaeological science, best known for his work on the chemical analysis of ancient glass. Born in the United States of America in 1929, Brill attended West Side High School in Newark, New Jersey, before going on to study for his B.S. degree at Upsala College, also New Jersey (Brill 1993a, Brill 2006, Getty Conservation Institute 2009). Having completed his Ph.D in Physical Chemistry at Rutgers University in 1954, Brill was to return to Upsala College to teach chemistry himself until 1960 when he joined the staff of the Corning Museum of Glass as their second research scientist (Corning Museum of Glass, 2009) Throughout his lengthy career at Corning, where a four-year directorship punctuated his time as a research scientist, Brill was a forerunner in the scientific investigation of glass, glazes and colorants, developing and challenging the usefulness of emerging techniques. His pioneering work with the application of lead and oxygen isotope analysis in archaeology led him occasionally to add the investigation of metal objects to his portfolio so that, together, his published works number more than 160 (Brill and Wampler 1967). Perhaps the most famous of these is his "Chemical Analyses of Early Glass", a sum of his 39 years of work and now a seminal reference guide in the field (Brill 1999) | https://en.wikipedia.org/wiki?curid=22222088 |
Robert H. Brill Brill is a strong proponent of interdisciplinary cooperation as well as the collaboration between scientists across the world, and has served since 1982 on the International Commission on Glass. Within this he founded TC17, the technical committee for the Archaeometry of Glass, which lists among its aims the ‘promotion of collaboration among glass specialists in widely separated countries’ and the stimulation and encouragement of glass scientists ‘in developing countries’ (Archaeometry of Glass 2005). His internationalism is aptly demonstrated by his study of glasses from around the world, with his attentions most recently being focused on those from the Silk Road. Here, as with other areas of Brill's remarkable career, it seems he was attracted by the lack of previous study and the need for further development in the field. Seeing a disparity between contemporary knowledge of glasses from the western world and those from East Asia, Brill was keen to add insight to a hitherto unexploited field and, as such, has gone on to contribute a great deal to Silk Road studies (Brill 1993b). The broad span of Brill's career allows this paper to provide only an abridged synopsis of his métier and published works to date | https://en.wikipedia.org/wiki?curid=22222088 |
Robert H. Brill Focusing on Brill's achievements during the decades after he joined the Corning Museum in February 1960, it aims to highlight areas in which Brill pioneered new techniques and improved existing ones, offering summaries of major publications and proposing sources the interested reader may turn to for more information (Brill 1999). The 1960s saw Brill beginning to develop the analytical techniques that would define the early years of his career at Corning, and yet the scope of his interest within glass remained vast. Indeed, 1961 saw Brill pen a letter to Nature with a colleague, that was a ‘bombshell’, according to Newton, in the field of glass-dating (1971, 3). Here Brill suggested that the rather enigmatic weathering crust found to form on buried glass objects over time could be used to date the object in a method rather similar to dendrochronology, using the separate layers of the shiny lamination (Brill 1961, Brill and Hood 1961, Newton 1971). Whilst in dendrochronology the tree-rings account simply for the tree's annual growth, in the weathering crust on glass Brill suggested the accumulation of a layer of laminate might respond to some kind of annual event of climatic change (Brill 1961) | https://en.wikipedia.org/wiki?curid=22222088 |
Robert H. Brill Unfortunately, despite the examples of the method's successful applications provided by Brill, such as the almost accurate count of 156 layers on a bottle-base from the York River submerged in 1781 and excavated in 1935, the technique largely failed to convince and did not see widespread adoption (Brill 1961, Newton 1971). The most important of these techniques would prove to be Brill's pioneering application of lead isotope analysis, hitherto used only in geology, to archaeological objects. Brill first presented this idea at the 1965 Seminar in Examination of Works of Art, held at the Museum of Fine Arts Boston, but the first widely published account of the method seems to be Brill and Wampler's 1967 article in the "American Journal of Archaeology". Here, Brill and Wampler outlined how the technique could be used to provenance the lead contents of archaeological objects to lead ore sources around the world, based on the isotopic signature of various leads, which relates them to ‘ores occurring in different geographical areas’ (1967, 63). These different areas have different signatures because they are of varying geological age, something reflected by the individual lead isotopes which form only after the radioactive decay of uranium and thorium (Brill et al. 1965, Brill and Wampler 1967). While the lead isotope ratios used for provenancing are different, they are not unique: areas geologically similar will yield similar lead isotope signatures (Brill 1970) | https://en.wikipedia.org/wiki?curid=22222088 |
Robert H. Brill Furthermore, if leads were salvaged and mixed in ancient times, the isotope ratio will be compromised (Brill 1970). Aside from these two limitations, there is little else that could affect the lead isotope reading an object would yield. As such, Brill's method was greeted enthusiastically and he went on to develop the technique, as well as oxygen isotope analysis, in his 1970 publication. Here he demonstrated how the technique could be used both to classify early glasses and to a certain extent characterize the ingredients from which they were made (1970, 143). Returning to 1965, this year saw Brill launch another important innovation in glass analysis, the comparison of interlaboratory experiments in order to verify analytical results (Brill 1965). ‘Originally inspired by a plea from W E S Turner’, according to Freestone, Brill first mooted his idea at the "VIIth International Congress on Glass", in Brussels (Brill 1965a, I. Freestone, "pers. comm." 2009). It wasn’t until the "VIIIth International Congress on Glass" in 1968, however, that Brill fully launched his concept of an ‘analytical round robin’, having distributed a number of reference glasses to be tested in different laboratories using a range of current techniques including X-ray fluorescence and neutron activation analysis (1968, 49). When discussing his motive for the experiment, Brill aptly stated: 'The truth is that the chemical analysis of glasses is a difficult undertaking and still remains in some senses an art' (1968, 49) | https://en.wikipedia.org/wiki?curid=22222088 |
Robert H. Brill By conducting the round robin experiment, Brill hoped the results gathered from different laboratories would help ‘correlate [...] earlier results’ and ‘calibrate future analyses in reference to one another’, as well as suggest which out of the analytical procedures used was the most accurate and effective (1968, 49). The results of the round robin were presented at the 'IXth International Congress on Glass' in 1971, and showed that, as Brill suspected, there was poor agreement between certain identified elements, and therefore these might be ‘troublesome’ generally across analyses (1971, 97). These included calcium, aluminium, lead and barium, among others (Brill 1971). Aside from their correctional potential, the results, from 45 different laboratories in 15 countries, also provided an enormous data set from which, Brill suggested, the participants could ‘evaluate their own methods and procedures against the findings of other analysts’ (1971, 97). At the time, Brill could hardly have suspected that the data would go on to have such great import, but Croegaard's generation of preferred glass compositions, from statistical analysis of the data, were used successfully by many people until Brill's own reference guide was published in 1999 (I. Freestone, 'pers. comm.', 2009) | https://en.wikipedia.org/wiki?curid=22222088 |
Robert H. Brill It should not be thought that Brill spent the entire decade ensconced in the Corning laboratory; he made various forays to the Middle East, including accompanying Wertime's 1968 survey of the ancient technologies of Iran, alongside other great minds such as the noted ceramicist, Frederick Matson (UCL Institute for Archaeo-Metallurgical Studies 2007). In the years 1963-1964, the Corning Museum of Glass and the University of Missouri, following a long history of excavation at the necropolis of Beth She'Arim, conducted an examination of a huge slab of glass, some 2000 years old, that had been languishing in an ancient cistern (Brill and Wosinski 1965). Brill cannot recall who first suggested this slab, measuring 3.4m by 1.94m, could be made of glass, but the only way to test it was to drill a core through its 45 cm thickness and analyse it (Brill 1967, Brill and Wosinski 1965). On analysis of the core, Brill found that the glass was devitrified and stained, and not very homogenous, with a presence of wollastonite crystals throughout (1965, 219.2) | https://en.wikipedia.org/wiki?curid=22222088 |
Robert H. Brill Investigation of the manufacture technology required to produce the slab, suggested that in order to produce such a slab of glass, it would have been necessary to heat over eleven tons of batch material, and sustain it at around 1050˚C for between five and ten days (Brill 1967)! His initial interpretation was that the glass must have been heated either from above or from the sides using a kind of tank furnace; a hypothesis that was proven accurate when excavation underneath the slab suggested it had been melted "in situ", in a tank whose floor was a bed of limestone blocks with a thin parting layer of clay (Brill and Wosinski 1965, Brill 1967). Brill's interpretation, that the slab and its surroundings suggest ‘some early form of reverberatory furnace’ was the first suggestion of the use of tank furnaces in early glassmaking (1967, 92). The evidence at Beth She’arim encouraged further innovative thought because whilst the slab represented glass production on a grand scale, no associated evidence for glass working was found. Brill had already suspected that historical glassmaking occurred in two phases, the heavy ‘engineering’ stage when the glass is formed from the batch ingredients and the ‘crafting’ stage when the glass is formed into artefacts (Brill, pers. comm., 2009). These stages could occur in combination at one location, or at two differing locales, and the time span of production after the initial glass melt is highly flexible | https://en.wikipedia.org/wiki?curid=22222088 |
Robert H. Brill For Brill, the idea of this ‘dual nature of all glassmaking’ was ‘crystallized’ at Beth She’Arim, where only the raw glass production was represented, and would be reinforced later by the contrasting evidence, where working was favoured over production, found at Jalame, as discussed below (Brill, pers. comm., 2009). Aside from the aforementioned published results of his analytical round robin and his lead and oxygen isotope studies in the early 1970s, the decade saw Brill publish comparatively little, perhaps due to his post as director at The Corning Museum of Glass. Those publications he did pen are largely concerned with the development of lead isotope analysis and are listed in the further reading section. Alas, before Brill could be named Director, however, the museum was to be blighted by an enormous flood, ‘possibly the greatest single catastrophe borne by an American museum’ according to Buechner, Brill's successor in 1976 (1977, 7). The flood was brought to Corning by Hurricane Agnes, a tropical storm that filled the Chemung River system to bursting until, on the morning of June 23, 1972, the river breached its banks and decimated the town (Martin and Edwards 1977). The Corning Glass Centre was under around twenty feet of water on the lower level's west side, while the museum itself was filled to a water-level of five feet and four inches (Martin and Edwards 1977) | https://en.wikipedia.org/wiki?curid=22222088 |
Robert H. Brill 528 of the museum's objects were damaged, the library's rare books were ruined and paper index systems, data and catalogues were all lost (Martin and Edwards 1977). In the wake of this destruction, Brill was named Director, so that his time holding this position, from 1972-1975, would be spent overseeing the complete restoration of the museum. Buechner praises how Brill 'painstakingly' prepared the insurance claim that would support the museum throughout the renovation process and facilitate the replacement of many wonderful objects (1977, 7). Under Brill's auspices, the Corning Museum of Glass was reopened just thirty-nine days after the event, on the 1st August, but it would be another four years before the collection and library were restored to their former glory (Buechner 1977). In 1982, Brill joined the International Commission on Glass, ‘the world’s leading organization of glass scientists and technologists’ according to the Corning Museum (2009). The International Commission functions through various technical committees, among which Brill saw an opening for TC17, the committee for the Archaeometry of Glass, which he founded shortly after joining. The main purpose of TC17, whose members met for the first time in Beijing in 1984, is ‘to bring together glass scientists, archaeologists and museum curators to present and discuss the results of research on early glass and glassmaking and on the conservation of historical glass objects’, as expressed in their mission statement (Archaeometry of Glass 2005) | https://en.wikipedia.org/wiki?curid=22222088 |
Robert H. Brill Brill was to chair this committee until 2004 and received the W E S Turner Award from the International Commission of Glass on his departure, in recognition of his contribution as founder (Corning Museum of Glass 2009). One of the on-running projects of the Corning Museum of Glass published the excavation report from their many field seasons at the ancient glass factory in Jalame, in Late Roman Palestine (Brill 1988, Schreurs and Brill 1984). Brill was called upon to conduct scientific investigations of the huge amount of material generated at the site, in order to exploit the full potential of the artefacts; after all, the site was being excavated specifically because of its role as a glass factory (Brill 1988). Of the vast quantity of glass fragments from Jalame, both vessel sherds and cullet, most were aqua and green and all were soda-lime-silica glasses melted in highly reducing conditions (Schreurs and Brill 1984). Where the melting conditions had been increasingly reducing, a ferri-sulfide chromophore complex was shown to have formed, thus changing the bluey-aqua colour of the glass to an olive, or even an amber shade (Schreurs and Brill 1984). Despite these colour variations, Brill's further chemical analysis showed the vessel glasses to be highly homogeneous in composition, apart from a clear divide where around 40 glasses demonstrated the intentional addition of manganese (Brill 1988) | https://en.wikipedia.org/wiki?curid=22222088 |
Robert H. Brill Brill conducted an investigation of the furnace at Jalame, nicknamed the Red Room, in which there was a mysterious absence of glass finds of any kind (Brill 1988). Whilst work at Beth She’Arim had eventually found there to be five firing chambers responsible for heating the one tank, the fragmentary remains at Jalame made it very difficult to interpret the furnace set-up, apart from the fact that they believed there to have been only one firing chamber (Brill 1988). In the late eighties Brill was to contribute various studies to the Institute of Nautical Archaeology, following the excavation of a number of exciting shipwrecks including the "Serçe Liman", and the "Ulu Burun" (Barnes et al. 1986, Brill 1989). Here Brill's own technique of lead isotope analysis was to provide a means for provenancing items aboard ship, and thus determine the ship's origin and her ports-of-call. The excavators of the "Serçe Liman" wanted to know whether she was Byzantine or Islamic, a complicated question for lead isotope analysis as the lead ores of the Eastern Mediterranean share geographical characteristics and therefore overlap (Barnes et al. 1986). Using 900 lead net sinkers divided into six loose groupings, Brill found groups III, V and VI to be Byzantine, that is with ores found in modern-day Turkey (Barnes et al. 1986) | https://en.wikipedia.org/wiki?curid=22222088 |
Robert H. Brill Group I, however, was taken to be most indicative of the ship's origin; this group contained net sinkers, but also two ceramic glazes and three glass vessels, all sharing virtually identical lead ores with only one isotopic match, ‘an ore from Anguran, northwest of Tehran’ according to Barnes et al. (1986, 7). Brill's submissions to the "XIVth International Congress on Glass", which took place in New Delhi in 1986, can be seen to represent the origins of his work on the Great Silk Road, the impressive trade route carrying goods from the East through India to Europe. Here, chemical analysis of Early Indian glasses would help Brill not just to determine the ingredients and techniques of production, but ‘to make certain broad generalizations as to regions or periods of manufacture’, and therefore to follow an object's movement along the trade route (1987, 1). For the XIVth Congress, Brill conducted atomic absorption spectroscopy (AAS) and optical emission spectroscopy (OES) on samples of 38 glasses from India, and the success of his method was made clear when he was able to separate 21 samples away from those made in the Middle East and Europe (Brill 1987). Here the glasses were shown to have mixed alkali compositions, a feature that is ‘rare among glasses from more westerly sources’, and therefore Brill concluded that they had definitely been manufactured in India (1987, 4) | https://en.wikipedia.org/wiki?curid=22222088 |
Robert H. Brill Brill also collaborated with Mckinnon to conduct chemical analyses of some glass samples from Sumatra, Indonesia, the results of which would be the ‘first data of their kind from this island’ (1987, 1). The results of the study, which also used samples from Java, another important location for the Silk Road, were hoped by McKinnon and Brill to ‘stimulate a greater awareness of glass in the economy [...] of ancient Sumatra and further new lines of research in the archaeology of the region’ (1987, 1). The beginning of the 1990s saw Brill accorded the Archaeological Institute of America's Pomerance Award for scientific contributions to archaeology; however the decade mostly reflects Brill's continuing dedication to Asian glasses and the study of the Silk Road (Archaeological Institute of America 2009). In "Scientific Research in Early Chinese Glass", Brill reflected that in comparison to the knowledge of glassmaking in the West, ‘little is known about Chinese glass and about the role it played in the overall unfolding of glass history on a worldwide basis’ (1991, vii). One reason for this is that glass was never produced in the East in such great quantities as it was in the West but also that archaeological Chinese glasses are often prone to problems (Brill 1991) | https://en.wikipedia.org/wiki?curid=22222088 |
Robert H. Brill The difficulties of analysing Chinese glasses were reflected later in the publication where, following the chemical investigation of 71 samples, Brill found that identifying the ‘basic formulation’, or ‘any of the primary batch materials’ of the glasses was still almost impossible (Brill et al. 1991). Brill had greater success in differentiating between Chinese glass samples when using lead isotope analysis, a method that has proven effective in the first instance of identifying Chinese glass as the leads used here are different from those anywhere else in the world (Brill, Barnes et al. 1991). Brill found his Chinese samples to fall into two distinct groups, possessing on one hand the highest, and on the other the lowest, lead isotope ratios he had "ever" encountered (Brill, Barnes et al. 1991). As such, he was able to show that despite the striking similarity in the glasses’ chemical composition and appearance, the ores from which their leads were sourced must have been from very geologically-different mines (Brill, Barnes et al. 1991). Brill conducted further investigations of ancient Asian glasses for the Nara Symposium on the Silk Road's maritime route in 1991, ‘to demonstrate [...] that chemical analyses can be useful for learning how glass was traded along the Desert, Steppe, and Maritime Routes of the Silk Road’ (1993a, 71), as well as providing a more technical discussion on glass and glassmaking in China for the Glass Art Society's Toledo Conference in 1993 (Brill 1993b) | https://en.wikipedia.org/wiki?curid=22222088 |
Robert H. Brill Further lead isotope analysis, this time on Chinese and central Asian pigments, was conducted with a larger team for the Getty's Conservation of Ancient Sites on the Silk Road, which saw Brill et al. launching studies that held incredible potential for understanding ‘chronological or stylistic differences among Buddhist cave paintings’, or ‘distinguish[ing] between original and repainted parts of individual works’ (1993, 371). In 1999, Brill published the sum of 39 years worth of results from his chemical investigations at Corning in two volumes of reference material with a third forthcoming (Brill 1999). Brill was reluctant to publish the data without any accompanying interpretation, but he felt that the most important factor was to quickly release the material into a wider sphere, made ‘readily accessible to the scientific community’ (1999, 8). Of Corning's 10,000 research artefacts, the master catalogue contains 6,400 samples, an abbreviated catalogue, or AbbCat, of which is presented in the two volumes (1999, 11). Nineteen geographical, typological or chronological categories of glass samples are recorded, spanning Brill's various research projects and collaborations, from Egypt to the East (Brill 1999). It also records the results of oxygen isotope analyses, reminding us that Brill was ever one for the integration of different investigative methods. Since 2000, Dr Brill's interest in Silk Road studies and ancient glass compositions has continued, but his publication rate has slowed somewhat | https://en.wikipedia.org/wiki?curid=22222088 |
Robert H. Brill His years of prolific publication, however, and his willingness to analyse glass from almost every situation have provided the archaeometry of glass with a bounty of reference material, as reflected by the "Chemical Analyses of Early Glasses". Despite his official retirement from the Corning Museum of Glass on May 31, 2008, he returned to the laboratory the next day and continues to work, showing no intention of enjoying a retirement proper any time soon (Brill, "pers. comm.", 2009). | https://en.wikipedia.org/wiki?curid=22222088 |
TBST In molecular biology, (or TTBS) is a mixture of tris-buffered saline (TBS) and Polysorbate 20 (also known as Tween 20). It is a buffer used for washing nitrocellulose membrane in western blotting and microtiter plate wells in ELISA assays. The following is a sample recipe for TBST: Adjust pH with HCl to pH 7.4–7.6 The simplest way to prepare a TBS-Tween solution is to use TBS-T tablets. They are formulated to give a ready to use solution upon dissolution in 500 ml of deionized water. | https://en.wikipedia.org/wiki?curid=22224112 |
Interferome is an online bioinformatics database of interferon-regulated genes (IRGs). These Interferon Regulated Genes are also known as Interferon Stimulated Genes (ISGs). The database contains information on type I (IFN alpha, beta), type II (IFN gamma) and type III (IFN lambda) regulated genes and is regularly updated. It is used by the interferon and cytokine research community both as an analysis tool and an information resource. Interferons were identified as antiviral proteins more than 50 years ago. However, their involvement in immunomodulation, cell proliferation, inflammation and other homeostatic processes has been since identified. These cytokines are used as therapeutics in many diseases such as chronic viral infections, cancer and multiple sclerosis. These interferons regulate the transcription of approximately 2000 genes in an interferon subtype, dose, cell type and stimulus dependent manner. This database of interferon regulated genes is an attempt at integrating information from high-throughput experiments and molecular biology databases to gain a detailed understanding of interferon biology. comprises the following data sets: offers many ways of searching and retrieving data from the database: is managed by a team at Monash University :Monash Institute of Medical Research and the University of Cambridge | https://en.wikipedia.org/wiki?curid=22228777 |
Hypoxic air technology for fire prevention Hypoxic air technology for fire prevention, also known as oxygen reduction system (ORS), is an active fire protection technique based on a permanent reduction of the oxygen concentration in the protected rooms. Unlike traditional fire suppression systems that usually extinguish fire after it is detected, hypoxic air is able to prevent fire. In a volume protected by hypoxic air, a normobaric hypoxic atmosphere is continuously retained: hypoxic means that the partial pressure of the oxygen is lower than at the sea level, normobaric means that the barometric pressure is equal to the barometric pressure at the sea level. Usually 1/4 to 1/2 of the oxygen contained in the air (that is, 5 to 10% of the air) is replaced by the same amount of nitrogen: as a consequence a hypoxic atmosphere containing around 15 Vol% of oxygen and 85 Vol% of nitrogen is created. In a normobaric hypoxic environment, common materials cannot ignite or burn. Thus, considering the fire triangle, a fire cannot occur because of the lack of sufficient oxygen. "However, at 15% oxygen level, risk for fire still exists, and the system cannot be seen as an alternative to extinguishing systems.". Air with a reduced oxygen content is injected to the protected volumes to lower the oxygen concentration until the desired oxygen concentration is reached | https://en.wikipedia.org/wiki?curid=22239522 |
Hypoxic air technology for fire prevention Then, because of air infiltration, the oxygen concentration inside the protected volumes rises: when it exceeds a certain threshold, low-oxygen air is again injected to the protected volumes until the desired oxygen concentration is reached. Oxygen sensors are installed in the protected volumes to monitor continuously the oxygen concentration. The exact oxygen level to retain in the protected volumes is determined after a careful assessment of materials, configurations and hazards. Tables are used which list ignition-limiting oxygen thresholds for some materials. Alternatively, the ignition-limiting threshold is determined by performing a proper ignition test described in BSI PAS 95:2011 - Hypoxic air fire prevention systems specification. Smoke detectors are installed in protected volumes because, similar to gas suppression systems, hypoxic air does not prevent smoldering and pyrolyzing processes. Air with low oxygen concentration is produced by hypoxic air generators, also known as air splitting units. There are three different types of hypoxic air generators: membrane-based, PSA-based and VSA-based ones. VSA-based hypoxic air generators have usually a lower energy consumption compared to PSA-based and membrane-based ones. Hypoxic air generators can be located inside or outside the protected rooms. Hypoxic air systems can be integrated with the building management system and can include systems to recover the heat generated by the hypoxic air generator that, otherwise, would be wasted | https://en.wikipedia.org/wiki?curid=22239522 |
Hypoxic air technology for fire prevention Air with low oxygen concentration is transported to the protected volumes through dedicated pipes or, more simply, via an existing ventilation system. In the latter case, dedicated pipes or ducts are not required. Hypoxic air fire prevention systems can also be used for purposes other than fire prevention, for example: Combining fire prevention, indoor climate and reduction of artefacts/food degradation is a completely new approach for a fire safety system. The benefits of preventing a fire instead of suppressing it makes hypoxic air especially suitable for applications where a fire would cause unacceptable damage and traditional fire suppression is unacceptable or unusable. Unlike traditional fire-suppression systems, dedicated pipes or nozzles are not required. In situations where the installation of a traditional firefighting system would pose severe problems, fire protection can be provided with hypoxic air. Hypoxic air for fire prevention suits best for: The reduction of artifact degradation and food deterioration is a plus for applications like food warehouses, storage and archives. The inherent simplicity of hypoxic air systems facilitates integration of sustainable building design and fire protection engineering. Fire-prevention systems which result in the oxygen content being less than 19.5% are not permitted for occupied spaces without providing employees supplemental respirators by federal regulation (OSHA) in the United States | https://en.wikipedia.org/wiki?curid=22239522 |
Hypoxic air technology for fire prevention However, hypoxic air is considered by some to be safe to breathe for most people. Medical studies have been undertaken on this topic. Angerer and Novak’s conclusion is that “"working environments with low oxygen concentrations to a minimum of 13% and normal barometric pressure do not impose a health hazard, provided that precautions are observed, comprising medical examinations and limitation of exposure time".” Küpper et al. say that oxygen concentration between 17.0–14.8% does not cause any risk for healthy people by hypoxia. It also does not cause risks for people with chronic diseases of moderate severity. The ability for strenuous work is reduced as the concentration decreases with the time that exertion can be sustained becoming very low below these levels, below around 17% it may be necessary to take breaks outside the environment if more than 6 hours is to be spent inside, especially if any physical exertion is performed Pressurized aircraft cabins are typically maintained at 75 kPa, the pressure found at altitude, resulting in an oxygen partial pressure of about 16 kPa, which is the same as a 15% oxygen concentration in a hypoxic-air application at sea-level pressure. However, passengers are sedentary and crew members have immediate access to supplemental oxygen. Hypoxic air is to be considered clean air and not contaminated air when assessing oxygen depletion hazards. Information relating access to the protected areas i.e | https://en.wikipedia.org/wiki?curid=22239522 |
Hypoxic air technology for fire prevention oxygen-reduced atmosphere are illustrated: Inspection body accreditation criteria are established according to ISO/IEC 17010 for third party verification of hypoxic air fire prevention system conformance to BSI PAS 95:2011 and VdS 3527en:2007 | https://en.wikipedia.org/wiki?curid=22239522 |
Selenium cycle The selenium cycle is a biological cycle of selenium similar to the cycles of carbon, nitrogen, and sulfur. Within the cycle, there are organisms which reduce the most oxidized form of the element and different organisms complete the cycle by oxidizing the reduced element to the initial state. In the selenium cycle it has been found that bacteria, fungi, and plants, especially species of "Astragalus", metabolize the most oxidized forms of selenium, selenate or selenite, to selenide. It is also thought that microorganisms may be able to oxidize selenium of valence zero to selenium of valence +6. Evidence for a selenium cycle is found through the study of selenium accumulator plants. These plants are found in semi-arid, seleniferous soils. The plants biosynthesize forms of organic selenium compounds and release the compounds into the soil when they decay. If the compounds were not oxidized, then an increase in organic selenium would be seen, but selenium in these areas is mainly inorganic. There are three fates of dissolved selenium in an aquatic ecosystem: 1. it can be absorbed or ingested by organisms; 2. it can bind with suspended solids or sediments; or 3. it can remain in free solution. Over time, most of the selenium is taken in by organisms or bound to other solids. As the suspended material settles, the selenium accumulates in the top layer of sediment. Due to the dynamic flow in an aquatic ecosystem, selenium is usually only in the sediments temporarily before being cycled back into the system | https://en.wikipedia.org/wiki?curid=22241441 |
Selenium cycle Selenium can be removed from the ecosystem and bound in sediment through natural processes of chemical and microbial reduction of the selenate form to the selenite form. The reduction is followed by adsorption to clay, reaction with iron species, and coprecipitation or settling. After selenium is in the sediment, other chemical and microbial reduction may occur, causing insoluble organic, mineral, elemental, or adsorbed selenium. Some organic forms may be released into the atmosphere from volatilization by chemical or microbial activity in the water and sediment or by direct release from plants. Immobilization processes effectively remove selenium from the ecosystem, especially in slow-moving or still-water areas. Selenium is made available to the food chain through four oxidation and methylation processes. The first process is oxidation and methylation of inorganic and organic selenium by plant roots and microorganisms. The second process is biological mixing and associated oxidation of sediments from the burrowing of benthic invertebrates and feeding of fish and wildlife. The third process is represented by physical movement and chemical oxidation from water circulation and mixing, such as current, wind, precipitation, and upwelling. The fourth process is from oxidation by plant photosynthesis. | https://en.wikipedia.org/wiki?curid=22241441 |
Photocatalytic water splitting is an artificial photosynthesis process with photocatalysis in a photoelectrochemical cell used for the dissociation of water into its constituent parts, hydrogen () and oxygen (), using either artificial or natural light. Theoretically, only light energy (photons), water, and a catalyst are needed. This topic is the focus of much research, but thus far no technology has been commercialized. Hydrogen fuel production has gained increased attention as public understanding of global warming has grown. Methods such as photocatalytic water splitting are being investigated to produce hydrogen, a clean-burning fuel. Water splitting holds particular promise since it utilizes water, an inexpensive renewable resource. has the simplicity of using a catalyst and sunlight to produce hydrogen out of water. When is split into and , the stoichiometric ratio of its products is 2:1: The process of water-splitting is a highly endothermic process (Δ"H" > 0). Water splitting occurs naturally in photosynthesis when the energy of a photon is absorbed and converted into the chemical energy through a complex biological pathway (Dolai's S-state diagrams. However, production of hydrogen from water requires large amounts of input energy, making it incompatible with existing energy generation. For this reason, most commercially produced hydrogen gas is produced from natural gas. Of the several requirements for an effective photocatalyst for water splitting, the potential difference (voltage) must be 1.23 V at 0 pH | https://en.wikipedia.org/wiki?curid=22242751 |
Photocatalytic water splitting Since the minimum band gap for successful water splitting at pH=0 is 1.23 eV, corresponding to light of 1008 nm, the electrochemical requirements can theoretically reach down into infrared light, albeit with negligible catalytic activity. These values are true only for a completely reversible reaction at standard temperature and pressure (1 bar and 25 °C). Theoretically, infrared light has enough energy to split water into hydrogen and oxygen; however, this reaction is very slow because the wavelength is greater than 750 nm. The potential must be less than 3.0 V to make efficient use of the energy present across the full spectrum of sunlight. Water splitting can transfer charges, but not be able to avoid corrosion for long term stability. Defects within crystalline photocatalysts can act as recombination sites, ultimately lowering efficiency. Under normal conditions, due to the transparency of water to visible light, photolysis can only occur with a radiation wavelength of 180 nm or shorter. We see then that, assuming a perfect system, the minimum energy input is 6.893 eV. Materials used in photocatalytic water splitting fulfill the band requirements outlined previously and typically have dopants and/or co-catalysts added to optimize their performance. A sample semiconductor with the proper band structure is titanium dioxide () | https://en.wikipedia.org/wiki?curid=22242751 |
Photocatalytic water splitting However, due to the relatively positive conduction band of , there is little driving force for production, so is typically used with a co-catalyst such as platinum (Pt) to increase the rate of production. It is routine to add co-catalysts to spur evolution in most photocatalysts due to the conduction band placement. Most semiconductors with suitable band structures to split water absorb mostly UV light; in order to absorb visible light, it is necessary to narrow the band gap. Since the conduction band is fairly close to the reference potential for formation, it is preferable to alter the valence band to move it closer to the potential for Photocatalysts can suffer from catalyst decay and recombination under operating conditions. Catalyst decay becomes a problem when using a sulfide-based photocatalyst such as cadmium sulfide (CdS), as the sulfide in the catalyst is oxidized to elemental sulfur at the same potentials used to split water. Thus, sulfide-based photocatalysts are not viable without sacrificial reagents such as sodium sulfide to replenish any sulfur lost, which effectively changes the main reaction to one of hydrogen evolution as opposed to water splitting. Recombination of the electron-hole pairs needed for photocatalysis can occur with any catalyst and is dependent on the defects and surface area of the catalyst; thus, a high degree of crystallinity is required to avoid recombination at the defects | https://en.wikipedia.org/wiki?curid=22242751 |
Photocatalytic water splitting The conversion of solar energy to hydrogen by means of photocatalysis is one of the most interesting ways to achieve clean and renewable energy systems. However, if this process is assisted by photocatalysts suspended directly in water instead of using a photovoltaic and electrolytic system the reaction is in just one step, and can therefore be more efficient. Photocatalysts must confirm to several key principles in order to be considered effective at water splitting. A key principle is that and evolution should occur in a stoichiometric 2:1 ratio; significant deviation could be due to a flaw in the experimental setup and/or a side reaction, both of which do not indicate a reliable photocatalyst for water splitting. The prime measure of photocatalyst effectiveness is quantum yield (QY), which is: This quantity is a reliable determination of how effective a photocatalyst is; however, it can be misleading due to varying experimental conditions. To assist in comparison, the rate of gas evolution can also be used; this method is more problematic on its own because it is not normalized, but it can be useful for a rough comparison and is consistently reported in the literature. Overall, the best photocatalyst has a high quantum yield and gives a high rate of gas evolution | https://en.wikipedia.org/wiki?curid=22242751 |
Photocatalytic water splitting The other important factor for a photocatalyst is the range of light absorbed; though UV-based photocatalysts will perform better per photon than visible light-based photocatalysts due to the higher photon energy, far more visible light reaches the Earth's surface than UV light. Thus, a less efficient photocatalyst that absorbs visible light may ultimately be more useful than a more efficient photocatalyst absorbing solely light with smaller wavelengths. The utility of a material for photocatalytic water splitting will typically be investigated for one of the two redox reactions at a time. To do this, a three component system is employed: a catalyst, a photosensitizer and a sacrificial electron acceptor such as persulfate when investigating water oxidation, and a sacrificial electron donor (for example triethylamine) when studying proton reduction. Employing sacrificial reagents in this manner simplifies research and prevents detrimental charge recombination reactions. Solid solutions with different Zn concentration (0.2 < "x" < 0.35) has been investigated in the production of hydrogen from aqueous solutions containing formula_2 as sacrificial reagents under visible light. Textural, structural and surface catalyst properties were determined by adsorption isotherms, UV–vis spectroscopy, SEM and XRD and related to the activity results in hydrogen production from water splitting under visible light irradiation | https://en.wikipedia.org/wiki?curid=22242751 |
Photocatalytic water splitting It was found that the crystallinity and energy band structure of the solid solutions depend on their Zn atomic concentration. The hydrogen production rate was found to increase gradually when the Zn concentration on photocatalysts increases from 0.2 to 0.3. Subsequent increase in the Zn fraction up to 0.35 leads to lower hydrogen production. Variation in photoactivity is analyzed in terms of changes in crystallinity, level of conduction band and light absorption ability of solid solutions derived from their Zn atomic concentration. , another catalyst activated by solely UV light and above, does not have the performance or quantum yield of :La. However, it does have the ability to split water without the assistance of cocatalysts and gives a quantum yield of 6.5% along with a water splitting rate of 1.21 mmol/h. This ability is due to the pillared structure of the photocatalyst, which involves pillars connected by triangle units. Loading with NiO did not assist the photocatalyst due to the highly active evolution sites. ()() has the highest quantum yield in visible light for visible light-based photocatalysts that do not utilize sacrificial reagents as of October 2008. The photocatalyst gives a quantum yield of 5.9% along with a water splitting rate of 0.4 mmol/h. Tuning the catalyst was done by increasing calcination temperatures for the final step in synthesizing the catalyst | https://en.wikipedia.org/wiki?curid=22242751 |
Photocatalytic water splitting Temperatures up to 600 °C helped to reduce the number of defects, though temperatures above 700 °C destroyed the local structure around zinc atoms and was thus undesirable. The treatment ultimately reduced the amount of surface Zn and O defects, which normally function as recombination sites, thus limiting photocatalytic activity. The catalyst was then loaded with at a rate of 2.5 wt % Rh and 2 wt% Cr to yield the best performance. Photocatalysts based on cobalt have been reported. Members are tris(bipyridine) cobalt(II), compounds of cobalt ligated to certain cyclic polyamines, and certain cobaloximes. In 2014 researchers announced an approach that connected a chromophore to part of a larger organic ring that surrounded a cobalt atom. The process is less efficient than using a platinum catalyst, cobalt is less expensive, potentially reducing total costs. The process uses one of two supramolecular assemblies based on Co(II)-templated coordination of (bpy = 2,2′-bipyridyl) analogues as photosensitizers and electron donors to a cobaloxime macrocycle. The Co(II) centres of both assemblies are high spin, in contrast to most previously described cobaloximes. Transient absorption optical spectroscopies include that charge recombination occurs through multiple ligand states present within the photosensitizer modules. Bismuth vanadate based systems have been demonstrated to have a record solar-to-hydrogen conversion efficiency of 5 | https://en.wikipedia.org/wiki?curid=22242751 |
Photocatalytic water splitting 2% (highest for metal-oxide photo-electrode) with the advantage of a very simple and cheap catalyst. Tungsten diselenide may have a role in future hydrogen fuel production, as a recent discovery in 2015 by scientists in Switzerland revealed that the compound's own photocatalytic properties might be a key to significantly more efficient electrolysis of water to produce hydrogen fuel. Systems based on the material class of III-V semiconductors, such as InGaP, enable currently the highest solar-to-hydrogen efficiencies of up to 14%. Long-term stability of these high-cost high-efficiency systems does, however, remain an issue. | https://en.wikipedia.org/wiki?curid=22242751 |
Comparison of nucleic acid simulation software This is a list of computer programs that are used for nucleic acids simulations. | https://en.wikipedia.org/wiki?curid=22253193 |
Pittcon Editors' Awards Pittcon Editors’ Awards honoured the best new products on show at the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, or Pittcon, for 20 years from 1996 having been established by Dr Gordon Wilkinson, managing editor of "Analytical Instrument Industry Report" (later "Instrumenta"). On 8 March 2015, the event returned to the Morial Convention Center in New Orleans and this was the last occasion when the awards were presented. The independent awards, which represented the results of an informal poll of leading editors, had become an important feature of the world's largest trade show for the laboratory equipment industry. Pittcon organisers and media center supported the scheme and provided details and photographs on the exhibition's Press and Media Information page. In 2016 the group of editors and journalists that formed the core of the judging panel reluctantly decided to discontinue the awards program citing gradually dwindling support from ever-busier media representatives. The awards were started because of the challenge that editors faced of effectively covering the trade show, which in 2015 hosted 925 exhibitors. New exhibitors at the Morial Convention Center totalled 130 companies. Walking past every booth at an event such as this represents a trek of over . Accredited media representatives, of whom there were more than 150 per year, were invited to list up to three new products on a nomination form provided on registration at the Media Center | https://en.wikipedia.org/wiki?curid=22255103 |
Pittcon Editors' Awards Editors were invited to attend a judging session towards the end of the trade show. They reviewed entries and voted on the nominated products. The only criterion was that products must have appeared at the exhibition for the first time, but winning products usually featured innovations in technology or industrial design, or enabled new analytical applications. Gold, Silver and Bronze winners were determined and plaques were awarded to the booth personnel of the winning companies on the final morning of the four-day exposition. Other nominated products received an Honourable Mention. Winners for the period 1996 to 2015, together with the names of their products, are listed below. Of the award winners, the majority were the largest instrument makers in the industry, but over 30 small companies or start-ups went home with awards, illustrating that editors were able to use their technical expertise to spot innovations irrespective of the marketing budgets of exhibitors. Company names are listed in the format used at the date of the award, although may have now changed as a result of change of ownership. Trademarks are acknowledged, but not indicated; readers should check corporate literature or websites for current intellectual property rights. Web links are only provided for award-winning products up to five years old. Products introduced earlier have usually been updated with more recent models. 2015: 2014: 2013: 2012: 2011: 2010: 2009: 2008: 2007: 2006: 2005: 2004: 2003: 2002: 2001: 2000: 1999: 1998: 1997: 1996: | https://en.wikipedia.org/wiki?curid=22255103 |
Silver bromate (AgBrO), is a poisonous, light and heat-sensitive, white powder. | https://en.wikipedia.org/wiki?curid=22262277 |
Serine/arginine-rich splicing factor 1 (SRSF1) also known as alternative splicing factor 1 (ASF1), pre-mRNA-splicing factor SF2 (SF2) or ASF1/SF2 is a protein that in humans is encoded by the "SRSF1" gene. ASF/SF2 is an essential sequence specific splicing factor involved in pre-mRNA splicing. SRSF1 is the gene that codes for ASF/SF2 and is found on chromosome 17. The resulting splicing factor is a protein of approximately 33 kDa. ASF/SF2 is necessary for all splicing reactions to occur, and influences splice site selection in a concentration-dependent manner, resulting in alternative splicing. In addition to being involved in the splicing process, ASF/SF2 also mediates post-splicing activities, such as mRNA nuclear export and translation. ASF/SF2 is an SR protein, and as such, contains two functional modules: an arginine-serine rich region (RS domain), where the bulk of ASF/SF2 regulation takes place, and two RNA recognition motifs (RRMs), through which ASF/SF2 interacts with RNA and other splicing factors. These modules have different functions within general splicing factor function. ASF/SF2 is an integral part of numerous components of the splicing process. ASF/SF2 is required for 5’ splice site cleavage and selection, and is capable of discriminating between cryptic and authentic splice sites. Subsequent lariat formation during the first chemical step of pre-mRNA splicing also requires ASF/SF2. ASF/SF2 promotes recruitment of the U1 snRNP to the 5’ splice site, and bridges the 5’ and 3’ splice sites to facilitate splicing reactions | https://en.wikipedia.org/wiki?curid=22264033 |
Serine/arginine-rich splicing factor 1 ASF/SF2 also associates with the U2 snRNP. During the reaction, ASF/SF2 promotes the use of intron proximal sites and hinders the use of intron distal sites, affecting alternative splicing. Alternative splicing is affected by ASF/SF2 in a concentration-dependent manner; differing concentrations of ASF/SF2 is a mechanism for alternative splicing regulation, and will result in differing amounts of product isoforms. ASF/SF2 accomplishes this regulation through direct or indirect binding to exonic splicing enhancer (ESE) sequences. ASF/SF2, in the presence of elF4E, promotes the initiation of translation of ribosome-bound mRNA by suppressing the activity of 4E-BP and recruiting molecules for further regulation of translation. ASF/SF2 interacts with the nuclear export protein TAP in a regulated manner, controlling the export of mature mRNA from the nucleus. An increase in cellular ASF/SF2 also will increase the efficiency of nonsense-mediated mRNA decay (NMD), favoring NMD that occurs before mRNA release from the nucleus over NMD that occurs after mRNA export from the nucleus to the cytoplasm. This shift in NMD caused by increased ASF/SF2 is accompanied by overall enhancement of the pioneer round of translation, through elF4E-bound mRNA translation and subsequent translationally active ribosomes, increased association of pioneer translation initiation complexes with ASF/SF2, and increased levels of active TAP | https://en.wikipedia.org/wiki?curid=22264033 |
Serine/arginine-rich splicing factor 1 ASF/SF2 has the ability to be phosphorylated at the serines in its RS domain by the SR specific protein kinase, SRPK1. SRPK1 and ASF/SF2 form an unusually stable complex of apparent K of 50nM. SRPK1 selectively phosphorylates up to twelve serines in the RS domain of ASF/SF2 through a directional and processive mechanism, moving from the C terminus to the N terminus. This multi-phosphorylation directs ASF/SF2 to the nucleus, influencing a number of protein-protein interactions associated with splicing. ASF/SF2’s function in export of mature mRNA from the nucleus is dependent on its phosphorylation state; dephosphorylation of ASF/SF2 facilitates binding to TAP, while phosphorylation directs ASF/SF2 to nuclear speckles. Both phosphorylation and dephosphorylation of ASF/SF2 are important and necessary for proper splicing to occur, as sequential phosphorylation and dephosphorylation marks the transitions between stages in the splicing process. In addition, hypophosphorylation and hyperphosphorylation of ASF/SF2 by Clk/Sty can lead to inhibition of splicing. ASF/SF2 is involved in genomic stability; it is thought that RNA Polymerase recruits ASF/SF2 to nascent RNA transcripts to impede formation of mutagenic DNA:RNA hybrid R-loop structures between the transcript and the template DNA. In this way, ASF/SF2 is protecting cells from the potential deleterious effects of transcription itself | https://en.wikipedia.org/wiki?curid=22264033 |
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